Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1 | ftrace - Function Tracer |
| 2 | ======================== |
| 3 | |
| 4 | Copyright 2008 Red Hat Inc. |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 5 | Author: Steven Rostedt <srostedt@redhat.com> |
| 6 | License: The GNU Free Documentation License, Version 1.2 |
Steven Rostedt | a97762a | 2008-07-31 12:40:52 -0400 | [diff] [blame] | 7 | (dual licensed under the GPL v2) |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 8 | Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, |
| 9 | John Kacur, and David Teigland. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 10 | |
Steven Rostedt | 42ec632 | 2008-11-03 15:18:56 -0500 | [diff] [blame] | 11 | Written for: 2.6.28-rc2 |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 12 | |
| 13 | Introduction |
| 14 | ------------ |
| 15 | |
| 16 | Ftrace is an internal tracer designed to help out developers and |
| 17 | designers of systems to find what is going on inside the kernel. |
| 18 | It can be used for debugging or analyzing latencies and performance |
| 19 | issues that take place outside of user-space. |
| 20 | |
| 21 | Although ftrace is the function tracer, it also includes an |
| 22 | infrastructure that allows for other types of tracing. Some of the |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 23 | tracers that are currently in ftrace include a tracer to trace |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 24 | context switches, the time it takes for a high priority task to |
| 25 | run after it was woken up, the time interrupts are disabled, and |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 26 | more (ftrace allows for tracer plugins, which means that the list of |
| 27 | tracers can always grow). |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 28 | |
| 29 | |
| 30 | The File System |
| 31 | --------------- |
| 32 | |
| 33 | Ftrace uses the debugfs file system to hold the control files as well |
| 34 | as the files to display output. |
| 35 | |
| 36 | To mount the debugfs system: |
| 37 | |
| 38 | # mkdir /debug |
| 39 | # mount -t debugfs nodev /debug |
| 40 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 41 | (Note: it is more common to mount at /sys/kernel/debug, but for simplicity |
| 42 | this document will use /debug) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 43 | |
| 44 | That's it! (assuming that you have ftrace configured into your kernel) |
| 45 | |
| 46 | After mounting the debugfs, you can see a directory called |
| 47 | "tracing". This directory contains the control and output files |
| 48 | of ftrace. Here is a list of some of the key files: |
| 49 | |
| 50 | |
| 51 | Note: all time values are in microseconds. |
| 52 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 53 | current_tracer: This is used to set or display the current tracer |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 54 | that is configured. |
| 55 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 56 | available_tracers: This holds the different types of tracers that |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 57 | have been compiled into the kernel. The tracers |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 58 | listed here can be configured by echoing their name |
| 59 | into current_tracer. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 60 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 61 | tracing_enabled: This sets or displays whether the current_tracer |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 62 | is activated and tracing or not. Echo 0 into this |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 63 | file to disable the tracer or 1 to enable it. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 64 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 65 | trace: This file holds the output of the trace in a human readable |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 66 | format (described below). |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 67 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 68 | latency_trace: This file shows the same trace but the information |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 69 | is organized more to display possible latencies |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 70 | in the system (described below). |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 71 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 72 | trace_pipe: The output is the same as the "trace" file but this |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 73 | file is meant to be streamed with live tracing. |
| 74 | Reads from this file will block until new data |
| 75 | is retrieved. Unlike the "trace" and "latency_trace" |
| 76 | files, this file is a consumer. This means reading |
| 77 | from this file causes sequential reads to display |
| 78 | more current data. Once data is read from this |
| 79 | file, it is consumed, and will not be read |
| 80 | again with a sequential read. The "trace" and |
| 81 | "latency_trace" files are static, and if the |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 82 | tracer is not adding more data, they will display |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 83 | the same information every time they are read. |
| 84 | |
Steven Rostedt | ee6bce5 | 2008-11-12 17:52:37 -0500 | [diff] [blame] | 85 | trace_options: This file lets the user control the amount of data |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 86 | that is displayed in one of the above output |
| 87 | files. |
| 88 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 89 | trace_max_latency: Some of the tracers record the max latency. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 90 | For example, the time interrupts are disabled. |
| 91 | This time is saved in this file. The max trace |
| 92 | will also be stored, and displayed by either |
| 93 | "trace" or "latency_trace". A new max trace will |
| 94 | only be recorded if the latency is greater than |
| 95 | the value in this file. (in microseconds) |
| 96 | |
Steven Rostedt | 1696b2b | 2008-11-13 00:09:35 -0500 | [diff] [blame] | 97 | buffer_size_kb: This sets or displays the number of kilobytes each CPU |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 98 | buffer can hold. The tracer buffers are the same size |
| 99 | for each CPU. The displayed number is the size of the |
Steven Rostedt | 1696b2b | 2008-11-13 00:09:35 -0500 | [diff] [blame] | 100 | CPU buffer and not total size of all buffers. The |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 101 | trace buffers are allocated in pages (blocks of memory |
| 102 | that the kernel uses for allocation, usually 4 KB in size). |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 103 | If the last page allocated has room for more bytes |
| 104 | than requested, the rest of the page will be used, |
| 105 | making the actual allocation bigger than requested. |
| 106 | (Note, the size may not be a multiple of the page size due |
| 107 | to buffer managment overhead.) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 108 | |
| 109 | This can only be updated when the current_tracer |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 110 | is set to "nop". |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 111 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 112 | tracing_cpumask: This is a mask that lets the user only trace |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 113 | on specified CPUS. The format is a hex string |
| 114 | representing the CPUS. |
| 115 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 116 | set_ftrace_filter: When dynamic ftrace is configured in (see the |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 117 | section below "dynamic ftrace"), the code is dynamically |
| 118 | modified (code text rewrite) to disable calling of the |
| 119 | function profiler (mcount). This lets tracing be configured |
| 120 | in with practically no overhead in performance. This also |
| 121 | has a side effect of enabling or disabling specific functions |
| 122 | to be traced. Echoing names of functions into this file |
| 123 | will limit the trace to only those functions. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 124 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 125 | set_ftrace_notrace: This has an effect opposite to that of |
| 126 | set_ftrace_filter. Any function that is added here will not |
| 127 | be traced. If a function exists in both set_ftrace_filter |
| 128 | and set_ftrace_notrace, the function will _not_ be traced. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 129 | |
Steven Rostedt | df4fc31 | 2008-11-26 00:16:23 -0500 | [diff] [blame] | 130 | set_ftrace_pid: Have the function tracer only trace a single thread. |
| 131 | |
Frederic Weisbecker | 985ec20 | 2009-02-18 06:35:34 +0100 | [diff] [blame^] | 132 | set_graph_function: Select the function where the trace have to start |
| 133 | with the function graph tracer (See the section |
| 134 | "dynamic ftrace" for more details). |
| 135 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 136 | available_filter_functions: This lists the functions that ftrace |
| 137 | has processed and can trace. These are the function |
| 138 | names that you can pass to "set_ftrace_filter" or |
| 139 | "set_ftrace_notrace". (See the section "dynamic ftrace" |
| 140 | below for more details.) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 141 | |
| 142 | |
| 143 | The Tracers |
| 144 | ----------- |
| 145 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 146 | Here is the list of current tracers that may be configured. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 147 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 148 | function - function tracer that uses mcount to trace all functions. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 149 | |
Frederic Weisbecker | 985ec20 | 2009-02-18 06:35:34 +0100 | [diff] [blame^] | 150 | function_graph_tracer - similar to the function tracer except that the |
| 151 | function tracer probes the functions on their entry whereas the |
| 152 | function graph tracer traces on both entry and exit of the |
| 153 | functions. It then provides the ability to draw a graph of |
| 154 | function calls like a primitive C code source. |
| 155 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 156 | sched_switch - traces the context switches between tasks. |
| 157 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 158 | irqsoff - traces the areas that disable interrupts and saves |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 159 | the trace with the longest max latency. |
| 160 | See tracing_max_latency. When a new max is recorded, |
| 161 | it replaces the old trace. It is best to view this |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 162 | trace via the latency_trace file. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 163 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 164 | preemptoff - Similar to irqsoff but traces and records the amount of |
| 165 | time for which preemption is disabled. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 166 | |
| 167 | preemptirqsoff - Similar to irqsoff and preemptoff, but traces and |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 168 | records the largest time for which irqs and/or preemption |
| 169 | is disabled. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 170 | |
| 171 | wakeup - Traces and records the max latency that it takes for |
| 172 | the highest priority task to get scheduled after |
| 173 | it has been woken up. |
| 174 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 175 | nop - This is not a tracer. To remove all tracers from tracing |
| 176 | simply echo "nop" into current_tracer. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 177 | |
Markus Metzger | e2ea539 | 2009-01-19 10:35:58 +0100 | [diff] [blame] | 178 | hw-branch-tracer - traces branches on all cpu's in a circular buffer. |
| 179 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 180 | |
| 181 | Examples of using the tracer |
| 182 | ---------------------------- |
| 183 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 184 | Here are typical examples of using the tracers when controlling them only |
| 185 | with the debugfs interface (without using any user-land utilities). |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 186 | |
| 187 | Output format: |
| 188 | -------------- |
| 189 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 190 | Here is an example of the output format of the file "trace" |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 191 | |
| 192 | -------- |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 193 | # tracer: function |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 194 | # |
| 195 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 196 | # | | | | | |
| 197 | bash-4251 [01] 10152.583854: path_put <-path_walk |
| 198 | bash-4251 [01] 10152.583855: dput <-path_put |
| 199 | bash-4251 [01] 10152.583855: _atomic_dec_and_lock <-dput |
| 200 | -------- |
| 201 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 202 | A header is printed with the tracer name that is represented by the trace. |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 203 | In this case the tracer is "function". Then a header showing the format. Task |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 204 | name "bash", the task PID "4251", the CPU that it was running on |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 205 | "01", the timestamp in <secs>.<usecs> format, the function name that was |
| 206 | traced "path_put" and the parent function that called this function |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 207 | "path_walk". The timestamp is the time at which the function was |
| 208 | entered. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 209 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 210 | The sched_switch tracer also includes tracing of task wakeups and |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 211 | context switches. |
| 212 | |
| 213 | ksoftirqd/1-7 [01] 1453.070013: 7:115:R + 2916:115:S |
| 214 | ksoftirqd/1-7 [01] 1453.070013: 7:115:R + 10:115:S |
| 215 | ksoftirqd/1-7 [01] 1453.070013: 7:115:R ==> 10:115:R |
| 216 | events/1-10 [01] 1453.070013: 10:115:S ==> 2916:115:R |
| 217 | kondemand/1-2916 [01] 1453.070013: 2916:115:S ==> 7:115:R |
| 218 | ksoftirqd/1-7 [01] 1453.070013: 7:115:S ==> 0:140:R |
| 219 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 220 | Wake ups are represented by a "+" and the context switches are shown as |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 221 | "==>". The format is: |
| 222 | |
| 223 | Context switches: |
| 224 | |
| 225 | Previous task Next Task |
| 226 | |
| 227 | <pid>:<prio>:<state> ==> <pid>:<prio>:<state> |
| 228 | |
| 229 | Wake ups: |
| 230 | |
| 231 | Current task Task waking up |
| 232 | |
| 233 | <pid>:<prio>:<state> + <pid>:<prio>:<state> |
| 234 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 235 | The prio is the internal kernel priority, which is the inverse of the |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 236 | priority that is usually displayed by user-space tools. Zero represents |
| 237 | the highest priority (99). Prio 100 starts the "nice" priorities with |
| 238 | 100 being equal to nice -20 and 139 being nice 19. The prio "140" is |
| 239 | reserved for the idle task which is the lowest priority thread (pid 0). |
| 240 | |
| 241 | |
| 242 | Latency trace format |
| 243 | -------------------- |
| 244 | |
| 245 | For traces that display latency times, the latency_trace file gives |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 246 | somewhat more information to see why a latency happened. Here is a typical |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 247 | trace. |
| 248 | |
| 249 | # tracer: irqsoff |
| 250 | # |
| 251 | irqsoff latency trace v1.1.5 on 2.6.26-rc8 |
| 252 | -------------------------------------------------------------------- |
| 253 | latency: 97 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 254 | ----------------- |
| 255 | | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0) |
| 256 | ----------------- |
| 257 | => started at: apic_timer_interrupt |
| 258 | => ended at: do_softirq |
| 259 | |
| 260 | # _------=> CPU# |
| 261 | # / _-----=> irqs-off |
| 262 | # | / _----=> need-resched |
| 263 | # || / _---=> hardirq/softirq |
| 264 | # ||| / _--=> preempt-depth |
| 265 | # |||| / |
| 266 | # ||||| delay |
| 267 | # cmd pid ||||| time | caller |
| 268 | # \ / ||||| \ | / |
| 269 | <idle>-0 0d..1 0us+: trace_hardirqs_off_thunk (apic_timer_interrupt) |
| 270 | <idle>-0 0d.s. 97us : __do_softirq (do_softirq) |
| 271 | <idle>-0 0d.s1 98us : trace_hardirqs_on (do_softirq) |
| 272 | |
| 273 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 274 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 275 | This shows that the current tracer is "irqsoff" tracing the time for which |
| 276 | interrupts were disabled. It gives the trace version and the version |
| 277 | of the kernel upon which this was executed on (2.6.26-rc8). Then it displays |
| 278 | the max latency in microsecs (97 us). The number of trace entries displayed |
| 279 | and the total number recorded (both are three: #3/3). The type of |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 280 | preemption that was used (PREEMPT). VP, KP, SP, and HP are always zero |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 281 | and are reserved for later use. #P is the number of online CPUS (#P:2). |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 282 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 283 | The task is the process that was running when the latency occurred. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 284 | (swapper pid: 0). |
| 285 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 286 | The start and stop (the functions in which the interrupts were disabled and |
| 287 | enabled respectively) that caused the latencies: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 288 | |
| 289 | apic_timer_interrupt is where the interrupts were disabled. |
| 290 | do_softirq is where they were enabled again. |
| 291 | |
| 292 | The next lines after the header are the trace itself. The header |
| 293 | explains which is which. |
| 294 | |
| 295 | cmd: The name of the process in the trace. |
| 296 | |
| 297 | pid: The PID of that process. |
| 298 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 299 | CPU#: The CPU which the process was running on. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 300 | |
| 301 | irqs-off: 'd' interrupts are disabled. '.' otherwise. |
Steven Rostedt | 9244489 | 2008-10-24 09:42:59 -0400 | [diff] [blame] | 302 | Note: If the architecture does not support a way to |
| 303 | read the irq flags variable, an 'X' will always |
| 304 | be printed here. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 305 | |
| 306 | need-resched: 'N' task need_resched is set, '.' otherwise. |
| 307 | |
| 308 | hardirq/softirq: |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 309 | 'H' - hard irq occurred inside a softirq. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 310 | 'h' - hard irq is running |
| 311 | 's' - soft irq is running |
| 312 | '.' - normal context. |
| 313 | |
| 314 | preempt-depth: The level of preempt_disabled |
| 315 | |
| 316 | The above is mostly meaningful for kernel developers. |
| 317 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 318 | time: This differs from the trace file output. The trace file output |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 319 | includes an absolute timestamp. The timestamp used by the |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 320 | latency_trace file is relative to the start of the trace. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 321 | |
| 322 | delay: This is just to help catch your eye a bit better. And |
| 323 | needs to be fixed to be only relative to the same CPU. |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 324 | The marks are determined by the difference between this |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 325 | current trace and the next trace. |
| 326 | '!' - greater than preempt_mark_thresh (default 100) |
| 327 | '+' - greater than 1 microsecond |
| 328 | ' ' - less than or equal to 1 microsecond. |
| 329 | |
| 330 | The rest is the same as the 'trace' file. |
| 331 | |
| 332 | |
Steven Rostedt | ee6bce5 | 2008-11-12 17:52:37 -0500 | [diff] [blame] | 333 | trace_options |
| 334 | ------------- |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 335 | |
Steven Rostedt | ee6bce5 | 2008-11-12 17:52:37 -0500 | [diff] [blame] | 336 | The trace_options file is used to control what gets printed in the trace |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 337 | output. To see what is available, simply cat the file: |
| 338 | |
Steven Rostedt | ee6bce5 | 2008-11-12 17:52:37 -0500 | [diff] [blame] | 339 | cat /debug/tracing/trace_options |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 340 | print-parent nosym-offset nosym-addr noverbose noraw nohex nobin \ |
Török Edwin | b54d3de | 2008-11-22 13:28:48 +0200 | [diff] [blame] | 341 | noblock nostacktrace nosched-tree nouserstacktrace nosym-userobj |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 342 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 343 | To disable one of the options, echo in the option prepended with "no". |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 344 | |
Steven Rostedt | ee6bce5 | 2008-11-12 17:52:37 -0500 | [diff] [blame] | 345 | echo noprint-parent > /debug/tracing/trace_options |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 346 | |
| 347 | To enable an option, leave off the "no". |
| 348 | |
Steven Rostedt | ee6bce5 | 2008-11-12 17:52:37 -0500 | [diff] [blame] | 349 | echo sym-offset > /debug/tracing/trace_options |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 350 | |
| 351 | Here are the available options: |
| 352 | |
| 353 | print-parent - On function traces, display the calling function |
| 354 | as well as the function being traced. |
| 355 | |
| 356 | print-parent: |
| 357 | bash-4000 [01] 1477.606694: simple_strtoul <-strict_strtoul |
| 358 | |
| 359 | noprint-parent: |
| 360 | bash-4000 [01] 1477.606694: simple_strtoul |
| 361 | |
| 362 | |
| 363 | sym-offset - Display not only the function name, but also the offset |
| 364 | in the function. For example, instead of seeing just |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 365 | "ktime_get", you will see "ktime_get+0xb/0x20". |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 366 | |
| 367 | sym-offset: |
| 368 | bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0 |
| 369 | |
| 370 | sym-addr - this will also display the function address as well as |
| 371 | the function name. |
| 372 | |
| 373 | sym-addr: |
| 374 | bash-4000 [01] 1477.606694: simple_strtoul <c0339346> |
| 375 | |
| 376 | verbose - This deals with the latency_trace file. |
| 377 | |
| 378 | bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \ |
| 379 | (+0.000ms): simple_strtoul (strict_strtoul) |
| 380 | |
| 381 | raw - This will display raw numbers. This option is best for use with |
| 382 | user applications that can translate the raw numbers better than |
| 383 | having it done in the kernel. |
| 384 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 385 | hex - Similar to raw, but the numbers will be in a hexadecimal format. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 386 | |
| 387 | bin - This will print out the formats in raw binary. |
| 388 | |
| 389 | block - TBD (needs update) |
| 390 | |
| 391 | stacktrace - This is one of the options that changes the trace itself. |
| 392 | When a trace is recorded, so is the stack of functions. |
| 393 | This allows for back traces of trace sites. |
| 394 | |
Török Edwin | 02b6751 | 2008-11-22 13:28:47 +0200 | [diff] [blame] | 395 | userstacktrace - This option changes the trace. |
| 396 | It records a stacktrace of the current userspace thread. |
| 397 | |
Török Edwin | b54d3de | 2008-11-22 13:28:48 +0200 | [diff] [blame] | 398 | sym-userobj - when user stacktrace are enabled, look up which object the |
| 399 | address belongs to, and print a relative address |
| 400 | This is especially useful when ASLR is on, otherwise you don't |
| 401 | get a chance to resolve the address to object/file/line after the app is no |
| 402 | longer running |
| 403 | |
| 404 | The lookup is performed when you read trace,trace_pipe,latency_trace. Example: |
| 405 | |
| 406 | a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 |
| 407 | x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] |
| 408 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 409 | sched-tree - TBD (any users??) |
| 410 | |
| 411 | |
| 412 | sched_switch |
| 413 | ------------ |
| 414 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 415 | This tracer simply records schedule switches. Here is an example |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 416 | of how to use it. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 417 | |
| 418 | # echo sched_switch > /debug/tracing/current_tracer |
| 419 | # echo 1 > /debug/tracing/tracing_enabled |
| 420 | # sleep 1 |
| 421 | # echo 0 > /debug/tracing/tracing_enabled |
| 422 | # cat /debug/tracing/trace |
| 423 | |
| 424 | # tracer: sched_switch |
| 425 | # |
| 426 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 427 | # | | | | | |
| 428 | bash-3997 [01] 240.132281: 3997:120:R + 4055:120:R |
| 429 | bash-3997 [01] 240.132284: 3997:120:R ==> 4055:120:R |
| 430 | sleep-4055 [01] 240.132371: 4055:120:S ==> 3997:120:R |
| 431 | bash-3997 [01] 240.132454: 3997:120:R + 4055:120:S |
| 432 | bash-3997 [01] 240.132457: 3997:120:R ==> 4055:120:R |
| 433 | sleep-4055 [01] 240.132460: 4055:120:D ==> 3997:120:R |
| 434 | bash-3997 [01] 240.132463: 3997:120:R + 4055:120:D |
| 435 | bash-3997 [01] 240.132465: 3997:120:R ==> 4055:120:R |
| 436 | <idle>-0 [00] 240.132589: 0:140:R + 4:115:S |
| 437 | <idle>-0 [00] 240.132591: 0:140:R ==> 4:115:R |
| 438 | ksoftirqd/0-4 [00] 240.132595: 4:115:S ==> 0:140:R |
| 439 | <idle>-0 [00] 240.132598: 0:140:R + 4:115:S |
| 440 | <idle>-0 [00] 240.132599: 0:140:R ==> 4:115:R |
| 441 | ksoftirqd/0-4 [00] 240.132603: 4:115:S ==> 0:140:R |
| 442 | sleep-4055 [01] 240.133058: 4055:120:S ==> 3997:120:R |
| 443 | [...] |
| 444 | |
| 445 | |
| 446 | As we have discussed previously about this format, the header shows |
| 447 | the name of the trace and points to the options. The "FUNCTION" |
| 448 | is a misnomer since here it represents the wake ups and context |
| 449 | switches. |
| 450 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 451 | The sched_switch file only lists the wake ups (represented with '+') |
| 452 | and context switches ('==>') with the previous task or current task |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 453 | first followed by the next task or task waking up. The format for both |
| 454 | of these is PID:KERNEL-PRIO:TASK-STATE. Remember that the KERNEL-PRIO |
| 455 | is the inverse of the actual priority with zero (0) being the highest |
| 456 | priority and the nice values starting at 100 (nice -20). Below is |
| 457 | a quick chart to map the kernel priority to user land priorities. |
| 458 | |
| 459 | Kernel priority: 0 to 99 ==> user RT priority 99 to 0 |
| 460 | Kernel priority: 100 to 139 ==> user nice -20 to 19 |
| 461 | Kernel priority: 140 ==> idle task priority |
| 462 | |
| 463 | The task states are: |
| 464 | |
| 465 | R - running : wants to run, may not actually be running |
| 466 | S - sleep : process is waiting to be woken up (handles signals) |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 467 | D - disk sleep (uninterruptible sleep) : process must be woken up |
| 468 | (ignores signals) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 469 | T - stopped : process suspended |
| 470 | t - traced : process is being traced (with something like gdb) |
| 471 | Z - zombie : process waiting to be cleaned up |
| 472 | X - unknown |
| 473 | |
| 474 | |
| 475 | ftrace_enabled |
| 476 | -------------- |
| 477 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 478 | The following tracers (listed below) give different output depending |
| 479 | on whether or not the sysctl ftrace_enabled is set. To set ftrace_enabled, |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 480 | one can either use the sysctl function or set it via the proc |
| 481 | file system interface. |
| 482 | |
| 483 | sysctl kernel.ftrace_enabled=1 |
| 484 | |
| 485 | or |
| 486 | |
| 487 | echo 1 > /proc/sys/kernel/ftrace_enabled |
| 488 | |
| 489 | To disable ftrace_enabled simply replace the '1' with '0' in |
| 490 | the above commands. |
| 491 | |
| 492 | When ftrace_enabled is set the tracers will also record the functions |
| 493 | that are within the trace. The descriptions of the tracers |
| 494 | will also show an example with ftrace enabled. |
| 495 | |
| 496 | |
| 497 | irqsoff |
| 498 | ------- |
| 499 | |
| 500 | When interrupts are disabled, the CPU can not react to any other |
| 501 | external event (besides NMIs and SMIs). This prevents the timer |
| 502 | interrupt from triggering or the mouse interrupt from letting the |
| 503 | kernel know of a new mouse event. The result is a latency with the |
| 504 | reaction time. |
| 505 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 506 | The irqsoff tracer tracks the time for which interrupts are disabled. |
| 507 | When a new maximum latency is hit, the tracer saves the trace leading up |
| 508 | to that latency point so that every time a new maximum is reached, the old |
| 509 | saved trace is discarded and the new trace is saved. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 510 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 511 | To reset the maximum, echo 0 into tracing_max_latency. Here is an |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 512 | example: |
| 513 | |
| 514 | # echo irqsoff > /debug/tracing/current_tracer |
| 515 | # echo 0 > /debug/tracing/tracing_max_latency |
| 516 | # echo 1 > /debug/tracing/tracing_enabled |
| 517 | # ls -ltr |
| 518 | [...] |
| 519 | # echo 0 > /debug/tracing/tracing_enabled |
| 520 | # cat /debug/tracing/latency_trace |
| 521 | # tracer: irqsoff |
| 522 | # |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 523 | irqsoff latency trace v1.1.5 on 2.6.26 |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 524 | -------------------------------------------------------------------- |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 525 | latency: 12 us, #3/3, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 526 | ----------------- |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 527 | | task: bash-3730 (uid:0 nice:0 policy:0 rt_prio:0) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 528 | ----------------- |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 529 | => started at: sys_setpgid |
| 530 | => ended at: sys_setpgid |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 531 | |
| 532 | # _------=> CPU# |
| 533 | # / _-----=> irqs-off |
| 534 | # | / _----=> need-resched |
| 535 | # || / _---=> hardirq/softirq |
| 536 | # ||| / _--=> preempt-depth |
| 537 | # |||| / |
| 538 | # ||||| delay |
| 539 | # cmd pid ||||| time | caller |
| 540 | # \ / ||||| \ | / |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 541 | bash-3730 1d... 0us : _write_lock_irq (sys_setpgid) |
| 542 | bash-3730 1d..1 1us+: _write_unlock_irq (sys_setpgid) |
| 543 | bash-3730 1d..2 14us : trace_hardirqs_on (sys_setpgid) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 544 | |
| 545 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 546 | Here we see that that we had a latency of 12 microsecs (which is |
| 547 | very good). The _write_lock_irq in sys_setpgid disabled interrupts. |
| 548 | The difference between the 12 and the displayed timestamp 14us occurred |
| 549 | because the clock was incremented between the time of recording the max |
| 550 | latency and the time of recording the function that had that latency. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 551 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 552 | Note the above example had ftrace_enabled not set. If we set the |
| 553 | ftrace_enabled, we get a much larger output: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 554 | |
| 555 | # tracer: irqsoff |
| 556 | # |
| 557 | irqsoff latency trace v1.1.5 on 2.6.26-rc8 |
| 558 | -------------------------------------------------------------------- |
| 559 | latency: 50 us, #101/101, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 560 | ----------------- |
| 561 | | task: ls-4339 (uid:0 nice:0 policy:0 rt_prio:0) |
| 562 | ----------------- |
| 563 | => started at: __alloc_pages_internal |
| 564 | => ended at: __alloc_pages_internal |
| 565 | |
| 566 | # _------=> CPU# |
| 567 | # / _-----=> irqs-off |
| 568 | # | / _----=> need-resched |
| 569 | # || / _---=> hardirq/softirq |
| 570 | # ||| / _--=> preempt-depth |
| 571 | # |||| / |
| 572 | # ||||| delay |
| 573 | # cmd pid ||||| time | caller |
| 574 | # \ / ||||| \ | / |
| 575 | ls-4339 0...1 0us+: get_page_from_freelist (__alloc_pages_internal) |
| 576 | ls-4339 0d..1 3us : rmqueue_bulk (get_page_from_freelist) |
| 577 | ls-4339 0d..1 3us : _spin_lock (rmqueue_bulk) |
| 578 | ls-4339 0d..1 4us : add_preempt_count (_spin_lock) |
| 579 | ls-4339 0d..2 4us : __rmqueue (rmqueue_bulk) |
| 580 | ls-4339 0d..2 5us : __rmqueue_smallest (__rmqueue) |
| 581 | ls-4339 0d..2 5us : __mod_zone_page_state (__rmqueue_smallest) |
| 582 | ls-4339 0d..2 6us : __rmqueue (rmqueue_bulk) |
| 583 | ls-4339 0d..2 6us : __rmqueue_smallest (__rmqueue) |
| 584 | ls-4339 0d..2 7us : __mod_zone_page_state (__rmqueue_smallest) |
| 585 | ls-4339 0d..2 7us : __rmqueue (rmqueue_bulk) |
| 586 | ls-4339 0d..2 8us : __rmqueue_smallest (__rmqueue) |
| 587 | [...] |
| 588 | ls-4339 0d..2 46us : __rmqueue_smallest (__rmqueue) |
| 589 | ls-4339 0d..2 47us : __mod_zone_page_state (__rmqueue_smallest) |
| 590 | ls-4339 0d..2 47us : __rmqueue (rmqueue_bulk) |
| 591 | ls-4339 0d..2 48us : __rmqueue_smallest (__rmqueue) |
| 592 | ls-4339 0d..2 48us : __mod_zone_page_state (__rmqueue_smallest) |
| 593 | ls-4339 0d..2 49us : _spin_unlock (rmqueue_bulk) |
| 594 | ls-4339 0d..2 49us : sub_preempt_count (_spin_unlock) |
| 595 | ls-4339 0d..1 50us : get_page_from_freelist (__alloc_pages_internal) |
| 596 | ls-4339 0d..2 51us : trace_hardirqs_on (__alloc_pages_internal) |
| 597 | |
| 598 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 599 | |
| 600 | Here we traced a 50 microsecond latency. But we also see all the |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 601 | functions that were called during that time. Note that by enabling |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 602 | function tracing, we incur an added overhead. This overhead may |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 603 | extend the latency times. But nevertheless, this trace has provided |
| 604 | some very helpful debugging information. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 605 | |
| 606 | |
| 607 | preemptoff |
| 608 | ---------- |
| 609 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 610 | When preemption is disabled, we may be able to receive interrupts but |
| 611 | the task cannot be preempted and a higher priority task must wait |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 612 | for preemption to be enabled again before it can preempt a lower |
| 613 | priority task. |
| 614 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 615 | The preemptoff tracer traces the places that disable preemption. |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 616 | Like the irqsoff tracer, it records the maximum latency for which preemption |
| 617 | was disabled. The control of preemptoff tracer is much like the irqsoff |
| 618 | tracer. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 619 | |
| 620 | # echo preemptoff > /debug/tracing/current_tracer |
| 621 | # echo 0 > /debug/tracing/tracing_max_latency |
| 622 | # echo 1 > /debug/tracing/tracing_enabled |
| 623 | # ls -ltr |
| 624 | [...] |
| 625 | # echo 0 > /debug/tracing/tracing_enabled |
| 626 | # cat /debug/tracing/latency_trace |
| 627 | # tracer: preemptoff |
| 628 | # |
| 629 | preemptoff latency trace v1.1.5 on 2.6.26-rc8 |
| 630 | -------------------------------------------------------------------- |
| 631 | latency: 29 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 632 | ----------------- |
| 633 | | task: sshd-4261 (uid:0 nice:0 policy:0 rt_prio:0) |
| 634 | ----------------- |
| 635 | => started at: do_IRQ |
| 636 | => ended at: __do_softirq |
| 637 | |
| 638 | # _------=> CPU# |
| 639 | # / _-----=> irqs-off |
| 640 | # | / _----=> need-resched |
| 641 | # || / _---=> hardirq/softirq |
| 642 | # ||| / _--=> preempt-depth |
| 643 | # |||| / |
| 644 | # ||||| delay |
| 645 | # cmd pid ||||| time | caller |
| 646 | # \ / ||||| \ | / |
| 647 | sshd-4261 0d.h. 0us+: irq_enter (do_IRQ) |
| 648 | sshd-4261 0d.s. 29us : _local_bh_enable (__do_softirq) |
| 649 | sshd-4261 0d.s1 30us : trace_preempt_on (__do_softirq) |
| 650 | |
| 651 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 652 | This has some more changes. Preemption was disabled when an interrupt |
| 653 | came in (notice the 'h'), and was enabled while doing a softirq. |
| 654 | (notice the 's'). But we also see that interrupts have been disabled |
| 655 | when entering the preempt off section and leaving it (the 'd'). |
| 656 | We do not know if interrupts were enabled in the mean time. |
| 657 | |
| 658 | # tracer: preemptoff |
| 659 | # |
| 660 | preemptoff latency trace v1.1.5 on 2.6.26-rc8 |
| 661 | -------------------------------------------------------------------- |
| 662 | latency: 63 us, #87/87, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 663 | ----------------- |
| 664 | | task: sshd-4261 (uid:0 nice:0 policy:0 rt_prio:0) |
| 665 | ----------------- |
| 666 | => started at: remove_wait_queue |
| 667 | => ended at: __do_softirq |
| 668 | |
| 669 | # _------=> CPU# |
| 670 | # / _-----=> irqs-off |
| 671 | # | / _----=> need-resched |
| 672 | # || / _---=> hardirq/softirq |
| 673 | # ||| / _--=> preempt-depth |
| 674 | # |||| / |
| 675 | # ||||| delay |
| 676 | # cmd pid ||||| time | caller |
| 677 | # \ / ||||| \ | / |
| 678 | sshd-4261 0d..1 0us : _spin_lock_irqsave (remove_wait_queue) |
| 679 | sshd-4261 0d..1 1us : _spin_unlock_irqrestore (remove_wait_queue) |
| 680 | sshd-4261 0d..1 2us : do_IRQ (common_interrupt) |
| 681 | sshd-4261 0d..1 2us : irq_enter (do_IRQ) |
| 682 | sshd-4261 0d..1 2us : idle_cpu (irq_enter) |
| 683 | sshd-4261 0d..1 3us : add_preempt_count (irq_enter) |
| 684 | sshd-4261 0d.h1 3us : idle_cpu (irq_enter) |
| 685 | sshd-4261 0d.h. 4us : handle_fasteoi_irq (do_IRQ) |
| 686 | [...] |
| 687 | sshd-4261 0d.h. 12us : add_preempt_count (_spin_lock) |
| 688 | sshd-4261 0d.h1 12us : ack_ioapic_quirk_irq (handle_fasteoi_irq) |
| 689 | sshd-4261 0d.h1 13us : move_native_irq (ack_ioapic_quirk_irq) |
| 690 | sshd-4261 0d.h1 13us : _spin_unlock (handle_fasteoi_irq) |
| 691 | sshd-4261 0d.h1 14us : sub_preempt_count (_spin_unlock) |
| 692 | sshd-4261 0d.h1 14us : irq_exit (do_IRQ) |
| 693 | sshd-4261 0d.h1 15us : sub_preempt_count (irq_exit) |
| 694 | sshd-4261 0d..2 15us : do_softirq (irq_exit) |
| 695 | sshd-4261 0d... 15us : __do_softirq (do_softirq) |
| 696 | sshd-4261 0d... 16us : __local_bh_disable (__do_softirq) |
| 697 | sshd-4261 0d... 16us+: add_preempt_count (__local_bh_disable) |
| 698 | sshd-4261 0d.s4 20us : add_preempt_count (__local_bh_disable) |
| 699 | sshd-4261 0d.s4 21us : sub_preempt_count (local_bh_enable) |
| 700 | sshd-4261 0d.s5 21us : sub_preempt_count (local_bh_enable) |
| 701 | [...] |
| 702 | sshd-4261 0d.s6 41us : add_preempt_count (__local_bh_disable) |
| 703 | sshd-4261 0d.s6 42us : sub_preempt_count (local_bh_enable) |
| 704 | sshd-4261 0d.s7 42us : sub_preempt_count (local_bh_enable) |
| 705 | sshd-4261 0d.s5 43us : add_preempt_count (__local_bh_disable) |
| 706 | sshd-4261 0d.s5 43us : sub_preempt_count (local_bh_enable_ip) |
| 707 | sshd-4261 0d.s6 44us : sub_preempt_count (local_bh_enable_ip) |
| 708 | sshd-4261 0d.s5 44us : add_preempt_count (__local_bh_disable) |
| 709 | sshd-4261 0d.s5 45us : sub_preempt_count (local_bh_enable) |
| 710 | [...] |
| 711 | sshd-4261 0d.s. 63us : _local_bh_enable (__do_softirq) |
| 712 | sshd-4261 0d.s1 64us : trace_preempt_on (__do_softirq) |
| 713 | |
| 714 | |
| 715 | The above is an example of the preemptoff trace with ftrace_enabled |
| 716 | set. Here we see that interrupts were disabled the entire time. |
| 717 | The irq_enter code lets us know that we entered an interrupt 'h'. |
| 718 | Before that, the functions being traced still show that it is not |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 719 | in an interrupt, but we can see from the functions themselves that |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 720 | this is not the case. |
| 721 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 722 | Notice that __do_softirq when called does not have a preempt_count. |
| 723 | It may seem that we missed a preempt enabling. What really happened |
| 724 | is that the preempt count is held on the thread's stack and we |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 725 | switched to the softirq stack (4K stacks in effect). The code |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 726 | does not copy the preempt count, but because interrupts are disabled, |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 727 | we do not need to worry about it. Having a tracer like this is good |
| 728 | for letting people know what really happens inside the kernel. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 729 | |
| 730 | |
| 731 | preemptirqsoff |
| 732 | -------------- |
| 733 | |
| 734 | Knowing the locations that have interrupts disabled or preemption |
| 735 | disabled for the longest times is helpful. But sometimes we would |
| 736 | like to know when either preemption and/or interrupts are disabled. |
| 737 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 738 | Consider the following code: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 739 | |
| 740 | local_irq_disable(); |
| 741 | call_function_with_irqs_off(); |
| 742 | preempt_disable(); |
| 743 | call_function_with_irqs_and_preemption_off(); |
| 744 | local_irq_enable(); |
| 745 | call_function_with_preemption_off(); |
| 746 | preempt_enable(); |
| 747 | |
| 748 | The irqsoff tracer will record the total length of |
| 749 | call_function_with_irqs_off() and |
| 750 | call_function_with_irqs_and_preemption_off(). |
| 751 | |
| 752 | The preemptoff tracer will record the total length of |
| 753 | call_function_with_irqs_and_preemption_off() and |
| 754 | call_function_with_preemption_off(). |
| 755 | |
| 756 | But neither will trace the time that interrupts and/or preemption |
| 757 | is disabled. This total time is the time that we can not schedule. |
| 758 | To record this time, use the preemptirqsoff tracer. |
| 759 | |
| 760 | Again, using this trace is much like the irqsoff and preemptoff tracers. |
| 761 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 762 | # echo preemptirqsoff > /debug/tracing/current_tracer |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 763 | # echo 0 > /debug/tracing/tracing_max_latency |
| 764 | # echo 1 > /debug/tracing/tracing_enabled |
| 765 | # ls -ltr |
| 766 | [...] |
| 767 | # echo 0 > /debug/tracing/tracing_enabled |
| 768 | # cat /debug/tracing/latency_trace |
| 769 | # tracer: preemptirqsoff |
| 770 | # |
| 771 | preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8 |
| 772 | -------------------------------------------------------------------- |
| 773 | latency: 293 us, #3/3, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 774 | ----------------- |
| 775 | | task: ls-4860 (uid:0 nice:0 policy:0 rt_prio:0) |
| 776 | ----------------- |
| 777 | => started at: apic_timer_interrupt |
| 778 | => ended at: __do_softirq |
| 779 | |
| 780 | # _------=> CPU# |
| 781 | # / _-----=> irqs-off |
| 782 | # | / _----=> need-resched |
| 783 | # || / _---=> hardirq/softirq |
| 784 | # ||| / _--=> preempt-depth |
| 785 | # |||| / |
| 786 | # ||||| delay |
| 787 | # cmd pid ||||| time | caller |
| 788 | # \ / ||||| \ | / |
| 789 | ls-4860 0d... 0us!: trace_hardirqs_off_thunk (apic_timer_interrupt) |
| 790 | ls-4860 0d.s. 294us : _local_bh_enable (__do_softirq) |
| 791 | ls-4860 0d.s1 294us : trace_preempt_on (__do_softirq) |
| 792 | |
| 793 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 794 | |
| 795 | The trace_hardirqs_off_thunk is called from assembly on x86 when |
| 796 | interrupts are disabled in the assembly code. Without the function |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 797 | tracing, we do not know if interrupts were enabled within the preemption |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 798 | points. We do see that it started with preemption enabled. |
| 799 | |
| 800 | Here is a trace with ftrace_enabled set: |
| 801 | |
| 802 | |
| 803 | # tracer: preemptirqsoff |
| 804 | # |
| 805 | preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8 |
| 806 | -------------------------------------------------------------------- |
| 807 | latency: 105 us, #183/183, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 808 | ----------------- |
| 809 | | task: sshd-4261 (uid:0 nice:0 policy:0 rt_prio:0) |
| 810 | ----------------- |
| 811 | => started at: write_chan |
| 812 | => ended at: __do_softirq |
| 813 | |
| 814 | # _------=> CPU# |
| 815 | # / _-----=> irqs-off |
| 816 | # | / _----=> need-resched |
| 817 | # || / _---=> hardirq/softirq |
| 818 | # ||| / _--=> preempt-depth |
| 819 | # |||| / |
| 820 | # ||||| delay |
| 821 | # cmd pid ||||| time | caller |
| 822 | # \ / ||||| \ | / |
| 823 | ls-4473 0.N.. 0us : preempt_schedule (write_chan) |
| 824 | ls-4473 0dN.1 1us : _spin_lock (schedule) |
| 825 | ls-4473 0dN.1 2us : add_preempt_count (_spin_lock) |
| 826 | ls-4473 0d..2 2us : put_prev_task_fair (schedule) |
| 827 | [...] |
| 828 | ls-4473 0d..2 13us : set_normalized_timespec (ktime_get_ts) |
| 829 | ls-4473 0d..2 13us : __switch_to (schedule) |
| 830 | sshd-4261 0d..2 14us : finish_task_switch (schedule) |
| 831 | sshd-4261 0d..2 14us : _spin_unlock_irq (finish_task_switch) |
| 832 | sshd-4261 0d..1 15us : add_preempt_count (_spin_lock_irqsave) |
| 833 | sshd-4261 0d..2 16us : _spin_unlock_irqrestore (hrtick_set) |
| 834 | sshd-4261 0d..2 16us : do_IRQ (common_interrupt) |
| 835 | sshd-4261 0d..2 17us : irq_enter (do_IRQ) |
| 836 | sshd-4261 0d..2 17us : idle_cpu (irq_enter) |
| 837 | sshd-4261 0d..2 18us : add_preempt_count (irq_enter) |
| 838 | sshd-4261 0d.h2 18us : idle_cpu (irq_enter) |
| 839 | sshd-4261 0d.h. 18us : handle_fasteoi_irq (do_IRQ) |
| 840 | sshd-4261 0d.h. 19us : _spin_lock (handle_fasteoi_irq) |
| 841 | sshd-4261 0d.h. 19us : add_preempt_count (_spin_lock) |
| 842 | sshd-4261 0d.h1 20us : _spin_unlock (handle_fasteoi_irq) |
| 843 | sshd-4261 0d.h1 20us : sub_preempt_count (_spin_unlock) |
| 844 | [...] |
| 845 | sshd-4261 0d.h1 28us : _spin_unlock (handle_fasteoi_irq) |
| 846 | sshd-4261 0d.h1 29us : sub_preempt_count (_spin_unlock) |
| 847 | sshd-4261 0d.h2 29us : irq_exit (do_IRQ) |
| 848 | sshd-4261 0d.h2 29us : sub_preempt_count (irq_exit) |
| 849 | sshd-4261 0d..3 30us : do_softirq (irq_exit) |
| 850 | sshd-4261 0d... 30us : __do_softirq (do_softirq) |
| 851 | sshd-4261 0d... 31us : __local_bh_disable (__do_softirq) |
| 852 | sshd-4261 0d... 31us+: add_preempt_count (__local_bh_disable) |
| 853 | sshd-4261 0d.s4 34us : add_preempt_count (__local_bh_disable) |
| 854 | [...] |
| 855 | sshd-4261 0d.s3 43us : sub_preempt_count (local_bh_enable_ip) |
| 856 | sshd-4261 0d.s4 44us : sub_preempt_count (local_bh_enable_ip) |
| 857 | sshd-4261 0d.s3 44us : smp_apic_timer_interrupt (apic_timer_interrupt) |
| 858 | sshd-4261 0d.s3 45us : irq_enter (smp_apic_timer_interrupt) |
| 859 | sshd-4261 0d.s3 45us : idle_cpu (irq_enter) |
| 860 | sshd-4261 0d.s3 46us : add_preempt_count (irq_enter) |
| 861 | sshd-4261 0d.H3 46us : idle_cpu (irq_enter) |
| 862 | sshd-4261 0d.H3 47us : hrtimer_interrupt (smp_apic_timer_interrupt) |
| 863 | sshd-4261 0d.H3 47us : ktime_get (hrtimer_interrupt) |
| 864 | [...] |
| 865 | sshd-4261 0d.H3 81us : tick_program_event (hrtimer_interrupt) |
| 866 | sshd-4261 0d.H3 82us : ktime_get (tick_program_event) |
| 867 | sshd-4261 0d.H3 82us : ktime_get_ts (ktime_get) |
| 868 | sshd-4261 0d.H3 83us : getnstimeofday (ktime_get_ts) |
| 869 | sshd-4261 0d.H3 83us : set_normalized_timespec (ktime_get_ts) |
| 870 | sshd-4261 0d.H3 84us : clockevents_program_event (tick_program_event) |
| 871 | sshd-4261 0d.H3 84us : lapic_next_event (clockevents_program_event) |
| 872 | sshd-4261 0d.H3 85us : irq_exit (smp_apic_timer_interrupt) |
| 873 | sshd-4261 0d.H3 85us : sub_preempt_count (irq_exit) |
| 874 | sshd-4261 0d.s4 86us : sub_preempt_count (irq_exit) |
| 875 | sshd-4261 0d.s3 86us : add_preempt_count (__local_bh_disable) |
| 876 | [...] |
| 877 | sshd-4261 0d.s1 98us : sub_preempt_count (net_rx_action) |
| 878 | sshd-4261 0d.s. 99us : add_preempt_count (_spin_lock_irq) |
| 879 | sshd-4261 0d.s1 99us+: _spin_unlock_irq (run_timer_softirq) |
| 880 | sshd-4261 0d.s. 104us : _local_bh_enable (__do_softirq) |
| 881 | sshd-4261 0d.s. 104us : sub_preempt_count (_local_bh_enable) |
| 882 | sshd-4261 0d.s. 105us : _local_bh_enable (__do_softirq) |
| 883 | sshd-4261 0d.s1 105us : trace_preempt_on (__do_softirq) |
| 884 | |
| 885 | |
| 886 | This is a very interesting trace. It started with the preemption of |
| 887 | the ls task. We see that the task had the "need_resched" bit set |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 888 | via the 'N' in the trace. Interrupts were disabled before the spin_lock |
| 889 | at the beginning of the trace. We see that a schedule took place to run |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 890 | sshd. When the interrupts were enabled, we took an interrupt. |
| 891 | On return from the interrupt handler, the softirq ran. We took another |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 892 | interrupt while running the softirq as we see from the capital 'H'. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 893 | |
| 894 | |
| 895 | wakeup |
| 896 | ------ |
| 897 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 898 | In a Real-Time environment it is very important to know the wakeup |
| 899 | time it takes for the highest priority task that is woken up to the |
| 900 | time that it executes. This is also known as "schedule latency". |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 901 | I stress the point that this is about RT tasks. It is also important |
| 902 | to know the scheduling latency of non-RT tasks, but the average |
| 903 | schedule latency is better for non-RT tasks. Tools like |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 904 | LatencyTop are more appropriate for such measurements. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 905 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 906 | Real-Time environments are interested in the worst case latency. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 907 | That is the longest latency it takes for something to happen, and |
| 908 | not the average. We can have a very fast scheduler that may only |
| 909 | have a large latency once in a while, but that would not work well |
| 910 | with Real-Time tasks. The wakeup tracer was designed to record |
| 911 | the worst case wakeups of RT tasks. Non-RT tasks are not recorded |
| 912 | because the tracer only records one worst case and tracing non-RT |
| 913 | tasks that are unpredictable will overwrite the worst case latency |
| 914 | of RT tasks. |
| 915 | |
| 916 | Since this tracer only deals with RT tasks, we will run this slightly |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 917 | differently than we did with the previous tracers. Instead of performing |
| 918 | an 'ls', we will run 'sleep 1' under 'chrt' which changes the |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 919 | priority of the task. |
| 920 | |
| 921 | # echo wakeup > /debug/tracing/current_tracer |
| 922 | # echo 0 > /debug/tracing/tracing_max_latency |
| 923 | # echo 1 > /debug/tracing/tracing_enabled |
| 924 | # chrt -f 5 sleep 1 |
| 925 | # echo 0 > /debug/tracing/tracing_enabled |
| 926 | # cat /debug/tracing/latency_trace |
| 927 | # tracer: wakeup |
| 928 | # |
| 929 | wakeup latency trace v1.1.5 on 2.6.26-rc8 |
| 930 | -------------------------------------------------------------------- |
| 931 | latency: 4 us, #2/2, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 932 | ----------------- |
| 933 | | task: sleep-4901 (uid:0 nice:0 policy:1 rt_prio:5) |
| 934 | ----------------- |
| 935 | |
| 936 | # _------=> CPU# |
| 937 | # / _-----=> irqs-off |
| 938 | # | / _----=> need-resched |
| 939 | # || / _---=> hardirq/softirq |
| 940 | # ||| / _--=> preempt-depth |
| 941 | # |||| / |
| 942 | # ||||| delay |
| 943 | # cmd pid ||||| time | caller |
| 944 | # \ / ||||| \ | / |
| 945 | <idle>-0 1d.h4 0us+: try_to_wake_up (wake_up_process) |
| 946 | <idle>-0 1d..4 4us : schedule (cpu_idle) |
| 947 | |
| 948 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 949 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 950 | Running this on an idle system, we see that it only took 4 microseconds |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 951 | to perform the task switch. Note, since the trace marker in the |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 952 | schedule is before the actual "switch", we stop the tracing when |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 953 | the recorded task is about to schedule in. This may change if |
| 954 | we add a new marker at the end of the scheduler. |
| 955 | |
| 956 | Notice that the recorded task is 'sleep' with the PID of 4901 and it |
| 957 | has an rt_prio of 5. This priority is user-space priority and not |
| 958 | the internal kernel priority. The policy is 1 for SCHED_FIFO and 2 |
| 959 | for SCHED_RR. |
| 960 | |
| 961 | Doing the same with chrt -r 5 and ftrace_enabled set. |
| 962 | |
| 963 | # tracer: wakeup |
| 964 | # |
| 965 | wakeup latency trace v1.1.5 on 2.6.26-rc8 |
| 966 | -------------------------------------------------------------------- |
| 967 | latency: 50 us, #60/60, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2) |
| 968 | ----------------- |
| 969 | | task: sleep-4068 (uid:0 nice:0 policy:2 rt_prio:5) |
| 970 | ----------------- |
| 971 | |
| 972 | # _------=> CPU# |
| 973 | # / _-----=> irqs-off |
| 974 | # | / _----=> need-resched |
| 975 | # || / _---=> hardirq/softirq |
| 976 | # ||| / _--=> preempt-depth |
| 977 | # |||| / |
| 978 | # ||||| delay |
| 979 | # cmd pid ||||| time | caller |
| 980 | # \ / ||||| \ | / |
| 981 | ksoftirq-7 1d.H3 0us : try_to_wake_up (wake_up_process) |
| 982 | ksoftirq-7 1d.H4 1us : sub_preempt_count (marker_probe_cb) |
| 983 | ksoftirq-7 1d.H3 2us : check_preempt_wakeup (try_to_wake_up) |
| 984 | ksoftirq-7 1d.H3 3us : update_curr (check_preempt_wakeup) |
| 985 | ksoftirq-7 1d.H3 4us : calc_delta_mine (update_curr) |
| 986 | ksoftirq-7 1d.H3 5us : __resched_task (check_preempt_wakeup) |
| 987 | ksoftirq-7 1d.H3 6us : task_wake_up_rt (try_to_wake_up) |
| 988 | ksoftirq-7 1d.H3 7us : _spin_unlock_irqrestore (try_to_wake_up) |
| 989 | [...] |
| 990 | ksoftirq-7 1d.H2 17us : irq_exit (smp_apic_timer_interrupt) |
| 991 | ksoftirq-7 1d.H2 18us : sub_preempt_count (irq_exit) |
| 992 | ksoftirq-7 1d.s3 19us : sub_preempt_count (irq_exit) |
| 993 | ksoftirq-7 1..s2 20us : rcu_process_callbacks (__do_softirq) |
| 994 | [...] |
| 995 | ksoftirq-7 1..s2 26us : __rcu_process_callbacks (rcu_process_callbacks) |
| 996 | ksoftirq-7 1d.s2 27us : _local_bh_enable (__do_softirq) |
| 997 | ksoftirq-7 1d.s2 28us : sub_preempt_count (_local_bh_enable) |
| 998 | ksoftirq-7 1.N.3 29us : sub_preempt_count (ksoftirqd) |
| 999 | ksoftirq-7 1.N.2 30us : _cond_resched (ksoftirqd) |
| 1000 | ksoftirq-7 1.N.2 31us : __cond_resched (_cond_resched) |
| 1001 | ksoftirq-7 1.N.2 32us : add_preempt_count (__cond_resched) |
| 1002 | ksoftirq-7 1.N.2 33us : schedule (__cond_resched) |
| 1003 | ksoftirq-7 1.N.2 33us : add_preempt_count (schedule) |
| 1004 | ksoftirq-7 1.N.3 34us : hrtick_clear (schedule) |
| 1005 | ksoftirq-7 1dN.3 35us : _spin_lock (schedule) |
| 1006 | ksoftirq-7 1dN.3 36us : add_preempt_count (_spin_lock) |
| 1007 | ksoftirq-7 1d..4 37us : put_prev_task_fair (schedule) |
| 1008 | ksoftirq-7 1d..4 38us : update_curr (put_prev_task_fair) |
| 1009 | [...] |
| 1010 | ksoftirq-7 1d..5 47us : _spin_trylock (tracing_record_cmdline) |
| 1011 | ksoftirq-7 1d..5 48us : add_preempt_count (_spin_trylock) |
| 1012 | ksoftirq-7 1d..6 49us : _spin_unlock (tracing_record_cmdline) |
| 1013 | ksoftirq-7 1d..6 49us : sub_preempt_count (_spin_unlock) |
| 1014 | ksoftirq-7 1d..4 50us : schedule (__cond_resched) |
| 1015 | |
| 1016 | The interrupt went off while running ksoftirqd. This task runs at |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1017 | SCHED_OTHER. Why did not we see the 'N' set early? This may be |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1018 | a harmless bug with x86_32 and 4K stacks. On x86_32 with 4K stacks |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1019 | configured, the interrupt and softirq run with their own stack. |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1020 | Some information is held on the top of the task's stack (need_resched |
| 1021 | and preempt_count are both stored there). The setting of the NEED_RESCHED |
| 1022 | bit is done directly to the task's stack, but the reading of the |
| 1023 | NEED_RESCHED is done by looking at the current stack, which in this case |
| 1024 | is the stack for the hard interrupt. This hides the fact that NEED_RESCHED |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1025 | has been set. We do not see the 'N' until we switch back to the task's |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1026 | assigned stack. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1027 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1028 | function |
| 1029 | -------- |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1030 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1031 | This tracer is the function tracer. Enabling the function tracer |
| 1032 | can be done from the debug file system. Make sure the ftrace_enabled is |
| 1033 | set; otherwise this tracer is a nop. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1034 | |
| 1035 | # sysctl kernel.ftrace_enabled=1 |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1036 | # echo function > /debug/tracing/current_tracer |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1037 | # echo 1 > /debug/tracing/tracing_enabled |
| 1038 | # usleep 1 |
| 1039 | # echo 0 > /debug/tracing/tracing_enabled |
| 1040 | # cat /debug/tracing/trace |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1041 | # tracer: function |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1042 | # |
| 1043 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1044 | # | | | | | |
| 1045 | bash-4003 [00] 123.638713: finish_task_switch <-schedule |
| 1046 | bash-4003 [00] 123.638714: _spin_unlock_irq <-finish_task_switch |
| 1047 | bash-4003 [00] 123.638714: sub_preempt_count <-_spin_unlock_irq |
| 1048 | bash-4003 [00] 123.638715: hrtick_set <-schedule |
| 1049 | bash-4003 [00] 123.638715: _spin_lock_irqsave <-hrtick_set |
| 1050 | bash-4003 [00] 123.638716: add_preempt_count <-_spin_lock_irqsave |
| 1051 | bash-4003 [00] 123.638716: _spin_unlock_irqrestore <-hrtick_set |
| 1052 | bash-4003 [00] 123.638717: sub_preempt_count <-_spin_unlock_irqrestore |
| 1053 | bash-4003 [00] 123.638717: hrtick_clear <-hrtick_set |
| 1054 | bash-4003 [00] 123.638718: sub_preempt_count <-schedule |
| 1055 | bash-4003 [00] 123.638718: sub_preempt_count <-preempt_schedule |
| 1056 | bash-4003 [00] 123.638719: wait_for_completion <-__stop_machine_run |
| 1057 | bash-4003 [00] 123.638719: wait_for_common <-wait_for_completion |
| 1058 | bash-4003 [00] 123.638720: _spin_lock_irq <-wait_for_common |
| 1059 | bash-4003 [00] 123.638720: add_preempt_count <-_spin_lock_irq |
| 1060 | [...] |
| 1061 | |
| 1062 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1063 | Note: function tracer uses ring buffers to store the above entries. |
| 1064 | The newest data may overwrite the oldest data. Sometimes using echo to |
| 1065 | stop the trace is not sufficient because the tracing could have overwritten |
| 1066 | the data that you wanted to record. For this reason, it is sometimes better to |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1067 | disable tracing directly from a program. This allows you to stop the |
| 1068 | tracing at the point that you hit the part that you are interested in. |
| 1069 | To disable the tracing directly from a C program, something like following |
| 1070 | code snippet can be used: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1071 | |
| 1072 | int trace_fd; |
| 1073 | [...] |
| 1074 | int main(int argc, char *argv[]) { |
| 1075 | [...] |
| 1076 | trace_fd = open("/debug/tracing/tracing_enabled", O_WRONLY); |
| 1077 | [...] |
| 1078 | if (condition_hit()) { |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1079 | write(trace_fd, "0", 1); |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1080 | } |
| 1081 | [...] |
| 1082 | } |
| 1083 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1084 | Note: Here we hard coded the path name. The debugfs mount is not |
| 1085 | guaranteed to be at /debug (and is more commonly at /sys/kernel/debug). |
| 1086 | For simple one time traces, the above is sufficent. For anything else, |
| 1087 | a search through /proc/mounts may be needed to find where the debugfs |
| 1088 | file-system is mounted. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1089 | |
Steven Rostedt | df4fc31 | 2008-11-26 00:16:23 -0500 | [diff] [blame] | 1090 | |
| 1091 | Single thread tracing |
| 1092 | --------------------- |
| 1093 | |
| 1094 | By writing into /debug/tracing/set_ftrace_pid you can trace a |
| 1095 | single thread. For example: |
| 1096 | |
| 1097 | # cat /debug/tracing/set_ftrace_pid |
| 1098 | no pid |
| 1099 | # echo 3111 > /debug/tracing/set_ftrace_pid |
| 1100 | # cat /debug/tracing/set_ftrace_pid |
| 1101 | 3111 |
| 1102 | # echo function > /debug/tracing/current_tracer |
| 1103 | # cat /debug/tracing/trace | head |
| 1104 | # tracer: function |
| 1105 | # |
| 1106 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1107 | # | | | | | |
| 1108 | yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return |
| 1109 | yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range |
| 1110 | yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel |
| 1111 | yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel |
| 1112 | yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll |
| 1113 | yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll |
| 1114 | # echo -1 > /debug/tracing/set_ftrace_pid |
| 1115 | # cat /debug/tracing/trace |head |
| 1116 | # tracer: function |
| 1117 | # |
| 1118 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1119 | # | | | | | |
| 1120 | ##### CPU 3 buffer started #### |
| 1121 | yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait |
| 1122 | yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry |
| 1123 | yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry |
| 1124 | yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit |
| 1125 | yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit |
| 1126 | |
| 1127 | If you want to trace a function when executing, you could use |
| 1128 | something like this simple program: |
| 1129 | |
| 1130 | #include <stdio.h> |
| 1131 | #include <stdlib.h> |
| 1132 | #include <sys/types.h> |
| 1133 | #include <sys/stat.h> |
| 1134 | #include <fcntl.h> |
| 1135 | #include <unistd.h> |
| 1136 | |
| 1137 | int main (int argc, char **argv) |
| 1138 | { |
| 1139 | if (argc < 1) |
| 1140 | exit(-1); |
| 1141 | |
| 1142 | if (fork() > 0) { |
| 1143 | int fd, ffd; |
| 1144 | char line[64]; |
| 1145 | int s; |
| 1146 | |
| 1147 | ffd = open("/debug/tracing/current_tracer", O_WRONLY); |
| 1148 | if (ffd < 0) |
| 1149 | exit(-1); |
| 1150 | write(ffd, "nop", 3); |
| 1151 | |
| 1152 | fd = open("/debug/tracing/set_ftrace_pid", O_WRONLY); |
| 1153 | s = sprintf(line, "%d\n", getpid()); |
| 1154 | write(fd, line, s); |
| 1155 | |
| 1156 | write(ffd, "function", 8); |
| 1157 | |
| 1158 | close(fd); |
| 1159 | close(ffd); |
| 1160 | |
| 1161 | execvp(argv[1], argv+1); |
| 1162 | } |
| 1163 | |
| 1164 | return 0; |
| 1165 | } |
| 1166 | |
Markus Metzger | e2ea539 | 2009-01-19 10:35:58 +0100 | [diff] [blame] | 1167 | |
| 1168 | hw-branch-tracer (x86 only) |
| 1169 | --------------------------- |
| 1170 | |
| 1171 | This tracer uses the x86 last branch tracing hardware feature to |
| 1172 | collect a branch trace on all cpus with relatively low overhead. |
| 1173 | |
| 1174 | The tracer uses a fixed-size circular buffer per cpu and only |
| 1175 | traces ring 0 branches. The trace file dumps that buffer in the |
| 1176 | following format: |
| 1177 | |
| 1178 | # tracer: hw-branch-tracer |
| 1179 | # |
| 1180 | # CPU# TO <- FROM |
| 1181 | 0 scheduler_tick+0xb5/0x1bf <- task_tick_idle+0x5/0x6 |
| 1182 | 2 run_posix_cpu_timers+0x2b/0x72a <- run_posix_cpu_timers+0x25/0x72a |
| 1183 | 0 scheduler_tick+0x139/0x1bf <- scheduler_tick+0xed/0x1bf |
| 1184 | 0 scheduler_tick+0x17c/0x1bf <- scheduler_tick+0x148/0x1bf |
| 1185 | 2 run_posix_cpu_timers+0x9e/0x72a <- run_posix_cpu_timers+0x5e/0x72a |
| 1186 | 0 scheduler_tick+0x1b6/0x1bf <- scheduler_tick+0x1aa/0x1bf |
| 1187 | |
| 1188 | |
| 1189 | The tracer may be used to dump the trace for the oops'ing cpu on a |
| 1190 | kernel oops into the system log. To enable this, ftrace_dump_on_oops |
| 1191 | must be set. To set ftrace_dump_on_oops, one can either use the sysctl |
| 1192 | function or set it via the proc system interface. |
| 1193 | |
| 1194 | sysctl kernel.ftrace_dump_on_oops=1 |
| 1195 | |
| 1196 | or |
| 1197 | |
| 1198 | echo 1 > /proc/sys/kernel/ftrace_dump_on_oops |
| 1199 | |
| 1200 | |
| 1201 | Here's an example of such a dump after a null pointer dereference in a |
| 1202 | kernel module: |
| 1203 | |
| 1204 | [57848.105921] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 |
| 1205 | [57848.106019] IP: [<ffffffffa0000006>] open+0x6/0x14 [oops] |
| 1206 | [57848.106019] PGD 2354e9067 PUD 2375e7067 PMD 0 |
| 1207 | [57848.106019] Oops: 0002 [#1] SMP |
| 1208 | [57848.106019] last sysfs file: /sys/devices/pci0000:00/0000:00:1e.0/0000:20:05.0/local_cpus |
| 1209 | [57848.106019] Dumping ftrace buffer: |
| 1210 | [57848.106019] --------------------------------- |
| 1211 | [...] |
| 1212 | [57848.106019] 0 chrdev_open+0xe6/0x165 <- cdev_put+0x23/0x24 |
| 1213 | [57848.106019] 0 chrdev_open+0x117/0x165 <- chrdev_open+0xfa/0x165 |
| 1214 | [57848.106019] 0 chrdev_open+0x120/0x165 <- chrdev_open+0x11c/0x165 |
| 1215 | [57848.106019] 0 chrdev_open+0x134/0x165 <- chrdev_open+0x12b/0x165 |
| 1216 | [57848.106019] 0 open+0x0/0x14 [oops] <- chrdev_open+0x144/0x165 |
| 1217 | [57848.106019] 0 page_fault+0x0/0x30 <- open+0x6/0x14 [oops] |
| 1218 | [57848.106019] 0 error_entry+0x0/0x5b <- page_fault+0x4/0x30 |
| 1219 | [57848.106019] 0 error_kernelspace+0x0/0x31 <- error_entry+0x59/0x5b |
| 1220 | [57848.106019] 0 error_sti+0x0/0x1 <- error_kernelspace+0x2d/0x31 |
| 1221 | [57848.106019] 0 page_fault+0x9/0x30 <- error_sti+0x0/0x1 |
| 1222 | [57848.106019] 0 do_page_fault+0x0/0x881 <- page_fault+0x1a/0x30 |
| 1223 | [...] |
| 1224 | [57848.106019] 0 do_page_fault+0x66b/0x881 <- is_prefetch+0x1ee/0x1f2 |
| 1225 | [57848.106019] 0 do_page_fault+0x6e0/0x881 <- do_page_fault+0x67a/0x881 |
| 1226 | [57848.106019] 0 oops_begin+0x0/0x96 <- do_page_fault+0x6e0/0x881 |
| 1227 | [57848.106019] 0 trace_hw_branch_oops+0x0/0x2d <- oops_begin+0x9/0x96 |
| 1228 | [...] |
| 1229 | [57848.106019] 0 ds_suspend_bts+0x2a/0xe3 <- ds_suspend_bts+0x1a/0xe3 |
| 1230 | [57848.106019] --------------------------------- |
| 1231 | [57848.106019] CPU 0 |
| 1232 | [57848.106019] Modules linked in: oops |
| 1233 | [57848.106019] Pid: 5542, comm: cat Tainted: G W 2.6.28 #23 |
| 1234 | [57848.106019] RIP: 0010:[<ffffffffa0000006>] [<ffffffffa0000006>] open+0x6/0x14 [oops] |
| 1235 | [57848.106019] RSP: 0018:ffff880235457d48 EFLAGS: 00010246 |
| 1236 | [...] |
| 1237 | |
| 1238 | |
Frederic Weisbecker | 985ec20 | 2009-02-18 06:35:34 +0100 | [diff] [blame^] | 1239 | function graph tracer |
| 1240 | --------------------------- |
| 1241 | |
| 1242 | This tracer is similar to the function tracer except that it probes |
| 1243 | a function on its entry and its exit. |
| 1244 | This is done by setting a dynamically allocated stack of return addresses on each |
| 1245 | task_struct. Then the tracer overwrites the return address of each function traced |
| 1246 | to set a custom probe. Thus the original return address is stored on the stack of return |
| 1247 | address in the task_struct. |
| 1248 | |
| 1249 | Probing on both extremities of a function leads to special features such as |
| 1250 | |
| 1251 | _ measure of function's time execution |
| 1252 | _ having a reliable call stack to draw function calls graph |
| 1253 | |
| 1254 | This tracer is useful in several situations: |
| 1255 | |
| 1256 | _ you want to find the reason of a strange kernel behavior and need to see |
| 1257 | what happens in detail on any areas (or specific ones). |
| 1258 | _ you are experiencing weird latencies but it's difficult to find its origin. |
| 1259 | _ you want to find quickly which path is taken by a specific function |
| 1260 | _ you just want to see what happens inside your kernel |
| 1261 | |
| 1262 | # tracer: function_graph |
| 1263 | # |
| 1264 | # CPU DURATION FUNCTION CALLS |
| 1265 | # | | | | | | | |
| 1266 | |
| 1267 | 0) | sys_open() { |
| 1268 | 0) | do_sys_open() { |
| 1269 | 0) | getname() { |
| 1270 | 0) | kmem_cache_alloc() { |
| 1271 | 0) 1.382 us | __might_sleep(); |
| 1272 | 0) 2.478 us | } |
| 1273 | 0) | strncpy_from_user() { |
| 1274 | 0) | might_fault() { |
| 1275 | 0) 1.389 us | __might_sleep(); |
| 1276 | 0) 2.553 us | } |
| 1277 | 0) 3.807 us | } |
| 1278 | 0) 7.876 us | } |
| 1279 | 0) | alloc_fd() { |
| 1280 | 0) 0.668 us | _spin_lock(); |
| 1281 | 0) 0.570 us | expand_files(); |
| 1282 | 0) 0.586 us | _spin_unlock(); |
| 1283 | |
| 1284 | |
| 1285 | There are several columns that can be dynamically enabled/disabled. |
| 1286 | You can use every combination of options you want, depending on your needs. |
| 1287 | |
| 1288 | _ The cpu number on which the function executed is default enabled. |
| 1289 | It is sometimes better to only trace one cpu (see tracing_cpu_mask file) |
| 1290 | or you might sometimes see unordered function calls while cpu tracing switch. |
| 1291 | |
| 1292 | hide: echo nofuncgraph-cpu > /debug/tracing/trace_options |
| 1293 | show: echo funcgraph-cpu > /debug/tracing/trace_options |
| 1294 | |
| 1295 | _ The duration (function's time of execution) is displayed on the closing bracket |
| 1296 | line of a function or on the same line than the current function in case of a leaf |
| 1297 | one. It is default enabled. |
| 1298 | |
| 1299 | hide: echo nofuncgraph-duration > /debug/tracing/trace_options |
| 1300 | show: echo funcgraph-duration > /debug/tracing/trace_options |
| 1301 | |
| 1302 | _ The overhead field precedes the duration one in case of reached duration thresholds. |
| 1303 | |
| 1304 | hide: echo nofuncgraph-overhead > /debug/tracing/trace_options |
| 1305 | show: echo funcgraph-overhead > /debug/tracing/trace_options |
| 1306 | depends on: funcgraph-duration |
| 1307 | |
| 1308 | ie: |
| 1309 | |
| 1310 | 0) | up_write() { |
| 1311 | 0) 0.646 us | _spin_lock_irqsave(); |
| 1312 | 0) 0.684 us | _spin_unlock_irqrestore(); |
| 1313 | 0) 3.123 us | } |
| 1314 | 0) 0.548 us | fput(); |
| 1315 | 0) + 58.628 us | } |
| 1316 | |
| 1317 | [...] |
| 1318 | |
| 1319 | 0) | putname() { |
| 1320 | 0) | kmem_cache_free() { |
| 1321 | 0) 0.518 us | __phys_addr(); |
| 1322 | 0) 1.757 us | } |
| 1323 | 0) 2.861 us | } |
| 1324 | 0) ! 115.305 us | } |
| 1325 | 0) ! 116.402 us | } |
| 1326 | |
| 1327 | + means that the function exceeded 10 usecs. |
| 1328 | ! means that the function exceeded 100 usecs. |
| 1329 | |
| 1330 | |
| 1331 | _ The task/pid field displays the thread cmdline and pid which executed the function. |
| 1332 | It is default disabled. |
| 1333 | |
| 1334 | hide: echo nofuncgraph-proc > /debug/tracing/trace_options |
| 1335 | show: echo funcgraph-proc > /debug/tracing/trace_options |
| 1336 | |
| 1337 | ie: |
| 1338 | |
| 1339 | # tracer: function_graph |
| 1340 | # |
| 1341 | # CPU TASK/PID DURATION FUNCTION CALLS |
| 1342 | # | | | | | | | | | |
| 1343 | 0) sh-4802 | | d_free() { |
| 1344 | 0) sh-4802 | | call_rcu() { |
| 1345 | 0) sh-4802 | | __call_rcu() { |
| 1346 | 0) sh-4802 | 0.616 us | rcu_process_gp_end(); |
| 1347 | 0) sh-4802 | 0.586 us | check_for_new_grace_period(); |
| 1348 | 0) sh-4802 | 2.899 us | } |
| 1349 | 0) sh-4802 | 4.040 us | } |
| 1350 | 0) sh-4802 | 5.151 us | } |
| 1351 | 0) sh-4802 | + 49.370 us | } |
| 1352 | |
| 1353 | |
| 1354 | _ The absolute time field is an absolute timestamp given by the clock since |
| 1355 | it started. A snapshot of this time is given on each entry/exit of functions |
| 1356 | |
| 1357 | hide: echo nofuncgraph-abstime > /debug/tracing/trace_options |
| 1358 | show: echo funcgraph-abstime > /debug/tracing/trace_options |
| 1359 | |
| 1360 | ie: |
| 1361 | |
| 1362 | # |
| 1363 | # TIME CPU DURATION FUNCTION CALLS |
| 1364 | # | | | | | | | | |
| 1365 | 360.774522 | 1) 0.541 us | } |
| 1366 | 360.774522 | 1) 4.663 us | } |
| 1367 | 360.774523 | 1) 0.541 us | __wake_up_bit(); |
| 1368 | 360.774524 | 1) 6.796 us | } |
| 1369 | 360.774524 | 1) 7.952 us | } |
| 1370 | 360.774525 | 1) 9.063 us | } |
| 1371 | 360.774525 | 1) 0.615 us | journal_mark_dirty(); |
| 1372 | 360.774527 | 1) 0.578 us | __brelse(); |
| 1373 | 360.774528 | 1) | reiserfs_prepare_for_journal() { |
| 1374 | 360.774528 | 1) | unlock_buffer() { |
| 1375 | 360.774529 | 1) | wake_up_bit() { |
| 1376 | 360.774529 | 1) | bit_waitqueue() { |
| 1377 | 360.774530 | 1) 0.594 us | __phys_addr(); |
| 1378 | |
| 1379 | |
| 1380 | You can put some comments on specific functions by using ftrace_printk() |
| 1381 | For example, if you want to put a comment inside the __might_sleep() function, |
| 1382 | you just have to include <linux/ftrace.h> and call ftrace_printk() inside __might_sleep() |
| 1383 | |
| 1384 | ftrace_printk("I'm a comment!\n") |
| 1385 | |
| 1386 | will produce: |
| 1387 | |
| 1388 | 1) | __might_sleep() { |
| 1389 | 1) | /* I'm a comment! */ |
| 1390 | 1) 1.449 us | } |
| 1391 | |
| 1392 | |
| 1393 | You might find other useful features for this tracer on the "dynamic ftrace" |
| 1394 | section such as tracing only specific functions or tasks. |
| 1395 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1396 | dynamic ftrace |
| 1397 | -------------- |
| 1398 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1399 | If CONFIG_DYNAMIC_FTRACE is set, the system will run with |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1400 | virtually no overhead when function tracing is disabled. The way |
| 1401 | this works is the mcount function call (placed at the start of |
| 1402 | every kernel function, produced by the -pg switch in gcc), starts |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1403 | of pointing to a simple return. (Enabling FTRACE will include the |
| 1404 | -pg switch in the compiling of the kernel.) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1405 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1406 | At compile time every C file object is run through the |
| 1407 | recordmcount.pl script (located in the scripts directory). This |
| 1408 | script will process the C object using objdump to find all the |
| 1409 | locations in the .text section that call mcount. (Note, only |
| 1410 | the .text section is processed, since processing other sections |
| 1411 | like .init.text may cause races due to those sections being freed). |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1412 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1413 | A new section called "__mcount_loc" is created that holds references |
| 1414 | to all the mcount call sites in the .text section. This section is |
| 1415 | compiled back into the original object. The final linker will add |
| 1416 | all these references into a single table. |
| 1417 | |
| 1418 | On boot up, before SMP is initialized, the dynamic ftrace code |
| 1419 | scans this table and updates all the locations into nops. It also |
| 1420 | records the locations, which are added to the available_filter_functions |
| 1421 | list. Modules are processed as they are loaded and before they are |
| 1422 | executed. When a module is unloaded, it also removes its functions from |
| 1423 | the ftrace function list. This is automatic in the module unload |
| 1424 | code, and the module author does not need to worry about it. |
| 1425 | |
| 1426 | When tracing is enabled, kstop_machine is called to prevent races |
| 1427 | with the CPUS executing code being modified (which can cause the |
| 1428 | CPU to do undesireable things), and the nops are patched back |
| 1429 | to calls. But this time, they do not call mcount (which is just |
| 1430 | a function stub). They now call into the ftrace infrastructure. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1431 | |
| 1432 | One special side-effect to the recording of the functions being |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1433 | traced is that we can now selectively choose which functions we |
| 1434 | wish to trace and which ones we want the mcount calls to remain as |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1435 | nops. |
| 1436 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1437 | Two files are used, one for enabling and one for disabling the tracing |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1438 | of specified functions. They are: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1439 | |
| 1440 | set_ftrace_filter |
| 1441 | |
| 1442 | and |
| 1443 | |
| 1444 | set_ftrace_notrace |
| 1445 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1446 | A list of available functions that you can add to these files is listed |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1447 | in: |
| 1448 | |
| 1449 | available_filter_functions |
| 1450 | |
| 1451 | # cat /debug/tracing/available_filter_functions |
| 1452 | put_prev_task_idle |
| 1453 | kmem_cache_create |
| 1454 | pick_next_task_rt |
| 1455 | get_online_cpus |
| 1456 | pick_next_task_fair |
| 1457 | mutex_lock |
| 1458 | [...] |
| 1459 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1460 | If I am only interested in sys_nanosleep and hrtimer_interrupt: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1461 | |
| 1462 | # echo sys_nanosleep hrtimer_interrupt \ |
| 1463 | > /debug/tracing/set_ftrace_filter |
| 1464 | # echo ftrace > /debug/tracing/current_tracer |
| 1465 | # echo 1 > /debug/tracing/tracing_enabled |
| 1466 | # usleep 1 |
| 1467 | # echo 0 > /debug/tracing/tracing_enabled |
| 1468 | # cat /debug/tracing/trace |
| 1469 | # tracer: ftrace |
| 1470 | # |
| 1471 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1472 | # | | | | | |
| 1473 | usleep-4134 [00] 1317.070017: hrtimer_interrupt <-smp_apic_timer_interrupt |
| 1474 | usleep-4134 [00] 1317.070111: sys_nanosleep <-syscall_call |
| 1475 | <idle>-0 [00] 1317.070115: hrtimer_interrupt <-smp_apic_timer_interrupt |
| 1476 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1477 | To see which functions are being traced, you can cat the file: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1478 | |
| 1479 | # cat /debug/tracing/set_ftrace_filter |
| 1480 | hrtimer_interrupt |
| 1481 | sys_nanosleep |
| 1482 | |
| 1483 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1484 | Perhaps this is not enough. The filters also allow simple wild cards. |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1485 | Only the following are currently available |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1486 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1487 | <match>* - will match functions that begin with <match> |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1488 | *<match> - will match functions that end with <match> |
| 1489 | *<match>* - will match functions that have <match> in it |
| 1490 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1491 | These are the only wild cards which are supported. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1492 | |
| 1493 | <match>*<match> will not work. |
| 1494 | |
walimis | c072c24 | 2008-11-28 12:21:19 +0800 | [diff] [blame] | 1495 | Note: It is better to use quotes to enclose the wild cards, otherwise |
| 1496 | the shell may expand the parameters into names of files in the local |
| 1497 | directory. |
| 1498 | |
| 1499 | # echo 'hrtimer_*' > /debug/tracing/set_ftrace_filter |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1500 | |
| 1501 | Produces: |
| 1502 | |
| 1503 | # tracer: ftrace |
| 1504 | # |
| 1505 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1506 | # | | | | | |
| 1507 | bash-4003 [00] 1480.611794: hrtimer_init <-copy_process |
| 1508 | bash-4003 [00] 1480.611941: hrtimer_start <-hrtick_set |
| 1509 | bash-4003 [00] 1480.611956: hrtimer_cancel <-hrtick_clear |
| 1510 | bash-4003 [00] 1480.611956: hrtimer_try_to_cancel <-hrtimer_cancel |
| 1511 | <idle>-0 [00] 1480.612019: hrtimer_get_next_event <-get_next_timer_interrupt |
| 1512 | <idle>-0 [00] 1480.612025: hrtimer_get_next_event <-get_next_timer_interrupt |
| 1513 | <idle>-0 [00] 1480.612032: hrtimer_get_next_event <-get_next_timer_interrupt |
| 1514 | <idle>-0 [00] 1480.612037: hrtimer_get_next_event <-get_next_timer_interrupt |
| 1515 | <idle>-0 [00] 1480.612382: hrtimer_get_next_event <-get_next_timer_interrupt |
| 1516 | |
| 1517 | |
| 1518 | Notice that we lost the sys_nanosleep. |
| 1519 | |
| 1520 | # cat /debug/tracing/set_ftrace_filter |
| 1521 | hrtimer_run_queues |
| 1522 | hrtimer_run_pending |
| 1523 | hrtimer_init |
| 1524 | hrtimer_cancel |
| 1525 | hrtimer_try_to_cancel |
| 1526 | hrtimer_forward |
| 1527 | hrtimer_start |
| 1528 | hrtimer_reprogram |
| 1529 | hrtimer_force_reprogram |
| 1530 | hrtimer_get_next_event |
| 1531 | hrtimer_interrupt |
| 1532 | hrtimer_nanosleep |
| 1533 | hrtimer_wakeup |
| 1534 | hrtimer_get_remaining |
| 1535 | hrtimer_get_res |
| 1536 | hrtimer_init_sleeper |
| 1537 | |
| 1538 | |
| 1539 | This is because the '>' and '>>' act just like they do in bash. |
| 1540 | To rewrite the filters, use '>' |
| 1541 | To append to the filters, use '>>' |
| 1542 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1543 | To clear out a filter so that all functions will be recorded again: |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1544 | |
| 1545 | # echo > /debug/tracing/set_ftrace_filter |
| 1546 | # cat /debug/tracing/set_ftrace_filter |
| 1547 | # |
| 1548 | |
| 1549 | Again, now we want to append. |
| 1550 | |
| 1551 | # echo sys_nanosleep > /debug/tracing/set_ftrace_filter |
| 1552 | # cat /debug/tracing/set_ftrace_filter |
| 1553 | sys_nanosleep |
walimis | c072c24 | 2008-11-28 12:21:19 +0800 | [diff] [blame] | 1554 | # echo 'hrtimer_*' >> /debug/tracing/set_ftrace_filter |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1555 | # cat /debug/tracing/set_ftrace_filter |
| 1556 | hrtimer_run_queues |
| 1557 | hrtimer_run_pending |
| 1558 | hrtimer_init |
| 1559 | hrtimer_cancel |
| 1560 | hrtimer_try_to_cancel |
| 1561 | hrtimer_forward |
| 1562 | hrtimer_start |
| 1563 | hrtimer_reprogram |
| 1564 | hrtimer_force_reprogram |
| 1565 | hrtimer_get_next_event |
| 1566 | hrtimer_interrupt |
| 1567 | sys_nanosleep |
| 1568 | hrtimer_nanosleep |
| 1569 | hrtimer_wakeup |
| 1570 | hrtimer_get_remaining |
| 1571 | hrtimer_get_res |
| 1572 | hrtimer_init_sleeper |
| 1573 | |
| 1574 | |
| 1575 | The set_ftrace_notrace prevents those functions from being traced. |
| 1576 | |
| 1577 | # echo '*preempt*' '*lock*' > /debug/tracing/set_ftrace_notrace |
| 1578 | |
| 1579 | Produces: |
| 1580 | |
| 1581 | # tracer: ftrace |
| 1582 | # |
| 1583 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1584 | # | | | | | |
| 1585 | bash-4043 [01] 115.281644: finish_task_switch <-schedule |
| 1586 | bash-4043 [01] 115.281645: hrtick_set <-schedule |
| 1587 | bash-4043 [01] 115.281645: hrtick_clear <-hrtick_set |
| 1588 | bash-4043 [01] 115.281646: wait_for_completion <-__stop_machine_run |
| 1589 | bash-4043 [01] 115.281647: wait_for_common <-wait_for_completion |
| 1590 | bash-4043 [01] 115.281647: kthread_stop <-stop_machine_run |
| 1591 | bash-4043 [01] 115.281648: init_waitqueue_head <-kthread_stop |
| 1592 | bash-4043 [01] 115.281648: wake_up_process <-kthread_stop |
| 1593 | bash-4043 [01] 115.281649: try_to_wake_up <-wake_up_process |
| 1594 | |
| 1595 | We can see that there's no more lock or preempt tracing. |
| 1596 | |
Frederic Weisbecker | 985ec20 | 2009-02-18 06:35:34 +0100 | [diff] [blame^] | 1597 | |
| 1598 | * Dynamic ftrace with the function graph tracer * |
| 1599 | |
| 1600 | |
| 1601 | Although what has been explained above concerns both the function tracer and |
| 1602 | the function_graph_tracer, the following concerns only the latter. |
| 1603 | |
| 1604 | If you want to trace only one function and all of its childs, you just have |
| 1605 | to echo its name on set_graph_function: |
| 1606 | |
| 1607 | echo __do_fault > set_graph_function |
| 1608 | |
| 1609 | will produce the following: |
| 1610 | |
| 1611 | 0) | __do_fault() { |
| 1612 | 0) | filemap_fault() { |
| 1613 | 0) | find_lock_page() { |
| 1614 | 0) 0.804 us | find_get_page(); |
| 1615 | 0) | __might_sleep() { |
| 1616 | 0) 1.329 us | } |
| 1617 | 0) 3.904 us | } |
| 1618 | 0) 4.979 us | } |
| 1619 | 0) 0.653 us | _spin_lock(); |
| 1620 | 0) 0.578 us | page_add_file_rmap(); |
| 1621 | 0) 0.525 us | native_set_pte_at(); |
| 1622 | 0) 0.585 us | _spin_unlock(); |
| 1623 | 0) | unlock_page() { |
| 1624 | 0) 0.541 us | page_waitqueue(); |
| 1625 | 0) 0.639 us | __wake_up_bit(); |
| 1626 | 0) 2.786 us | } |
| 1627 | 0) + 14.237 us | } |
| 1628 | 0) | __do_fault() { |
| 1629 | 0) | filemap_fault() { |
| 1630 | 0) | find_lock_page() { |
| 1631 | 0) 0.698 us | find_get_page(); |
| 1632 | 0) | __might_sleep() { |
| 1633 | 0) 1.412 us | } |
| 1634 | 0) 3.950 us | } |
| 1635 | 0) 5.098 us | } |
| 1636 | 0) 0.631 us | _spin_lock(); |
| 1637 | 0) 0.571 us | page_add_file_rmap(); |
| 1638 | 0) 0.526 us | native_set_pte_at(); |
| 1639 | 0) 0.586 us | _spin_unlock(); |
| 1640 | 0) | unlock_page() { |
| 1641 | 0) 0.533 us | page_waitqueue(); |
| 1642 | 0) 0.638 us | __wake_up_bit(); |
| 1643 | 0) 2.793 us | } |
| 1644 | 0) + 14.012 us | } |
| 1645 | |
| 1646 | You can also select several functions: |
| 1647 | |
| 1648 | echo sys_open > set_graph_function |
| 1649 | echo sys_close >> set_graph_function |
| 1650 | |
| 1651 | Now if you want to go back to trace all functions |
| 1652 | |
| 1653 | echo > set_graph_function |
| 1654 | |
| 1655 | |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1656 | trace_pipe |
| 1657 | ---------- |
| 1658 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1659 | The trace_pipe outputs the same content as the trace file, but the effect |
| 1660 | on the tracing is different. Every read from trace_pipe is consumed. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1661 | This means that subsequent reads will be different. The trace |
| 1662 | is live. |
| 1663 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1664 | # echo function > /debug/tracing/current_tracer |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1665 | # cat /debug/tracing/trace_pipe > /tmp/trace.out & |
| 1666 | [1] 4153 |
| 1667 | # echo 1 > /debug/tracing/tracing_enabled |
| 1668 | # usleep 1 |
| 1669 | # echo 0 > /debug/tracing/tracing_enabled |
| 1670 | # cat /debug/tracing/trace |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1671 | # tracer: function |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1672 | # |
| 1673 | # TASK-PID CPU# TIMESTAMP FUNCTION |
| 1674 | # | | | | | |
| 1675 | |
| 1676 | # |
| 1677 | # cat /tmp/trace.out |
| 1678 | bash-4043 [00] 41.267106: finish_task_switch <-schedule |
| 1679 | bash-4043 [00] 41.267106: hrtick_set <-schedule |
| 1680 | bash-4043 [00] 41.267107: hrtick_clear <-hrtick_set |
| 1681 | bash-4043 [00] 41.267108: wait_for_completion <-__stop_machine_run |
| 1682 | bash-4043 [00] 41.267108: wait_for_common <-wait_for_completion |
| 1683 | bash-4043 [00] 41.267109: kthread_stop <-stop_machine_run |
| 1684 | bash-4043 [00] 41.267109: init_waitqueue_head <-kthread_stop |
| 1685 | bash-4043 [00] 41.267110: wake_up_process <-kthread_stop |
| 1686 | bash-4043 [00] 41.267110: try_to_wake_up <-wake_up_process |
| 1687 | bash-4043 [00] 41.267111: select_task_rq_rt <-try_to_wake_up |
| 1688 | |
| 1689 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1690 | Note, reading the trace_pipe file will block until more input is added. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1691 | By changing the tracer, trace_pipe will issue an EOF. We needed |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1692 | to set the function tracer _before_ we "cat" the trace_pipe file. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1693 | |
| 1694 | |
| 1695 | trace entries |
| 1696 | ------------- |
| 1697 | |
| 1698 | Having too much or not enough data can be troublesome in diagnosing |
Steven Rostedt | a94c80e | 2008-11-12 17:52:36 -0500 | [diff] [blame] | 1699 | an issue in the kernel. The file buffer_size_kb is used to modify |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1700 | the size of the internal trace buffers. The number listed |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1701 | is the number of entries that can be recorded per CPU. To know |
| 1702 | the full size, multiply the number of possible CPUS with the |
| 1703 | number of entries. |
| 1704 | |
Steven Rostedt | a94c80e | 2008-11-12 17:52:36 -0500 | [diff] [blame] | 1705 | # cat /debug/tracing/buffer_size_kb |
Steven Rostedt | 1696b2b | 2008-11-13 00:09:35 -0500 | [diff] [blame] | 1706 | 1408 (units kilobytes) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1707 | |
Steven Rostedt | a41eeba | 2008-07-14 16:41:12 -0400 | [diff] [blame] | 1708 | Note, to modify this, you must have tracing completely disabled. To do that, |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1709 | echo "nop" into the current_tracer. If the current_tracer is not set |
| 1710 | to "nop", an EINVAL error will be returned. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1711 | |
Steven Rostedt | 9b803c0 | 2008-11-03 15:15:08 -0500 | [diff] [blame] | 1712 | # echo nop > /debug/tracing/current_tracer |
Steven Rostedt | 1696b2b | 2008-11-13 00:09:35 -0500 | [diff] [blame] | 1713 | # echo 10000 > /debug/tracing/buffer_size_kb |
Steven Rostedt | a94c80e | 2008-11-12 17:52:36 -0500 | [diff] [blame] | 1714 | # cat /debug/tracing/buffer_size_kb |
Steven Rostedt | 1696b2b | 2008-11-13 00:09:35 -0500 | [diff] [blame] | 1715 | 10000 (units kilobytes) |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1716 | |
Steven Rostedt | f2d9c74 | 2008-07-15 10:57:33 -0400 | [diff] [blame] | 1717 | The number of pages which will be allocated is limited to a percentage |
| 1718 | of available memory. Allocating too much will produce an error. |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1719 | |
Steven Rostedt | a94c80e | 2008-11-12 17:52:36 -0500 | [diff] [blame] | 1720 | # echo 1000000000000 > /debug/tracing/buffer_size_kb |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1721 | -bash: echo: write error: Cannot allocate memory |
Steven Rostedt | a94c80e | 2008-11-12 17:52:36 -0500 | [diff] [blame] | 1722 | # cat /debug/tracing/buffer_size_kb |
Steven Rostedt | eb6d42e | 2008-07-10 12:46:01 -0400 | [diff] [blame] | 1723 | 85 |
| 1724 | |