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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/* calibrate.c: default delay calibration
2 *
3 * Excised from init/main.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
Tim Schmielaucd354f12007-02-14 00:33:14 -08007#include <linux/jiffies.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07008#include <linux/delay.h>
9#include <linux/init.h>
Andrew Morton941e4922008-02-06 01:36:42 -080010#include <linux/timex.h>
Alok Kataria3da757d2008-06-20 15:06:33 -070011#include <linux/smp.h>
Sameer Nanda7afe1842011-07-25 17:13:29 -070012#include <linux/percpu.h>
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070013
Alok Katariaf3f31492008-06-23 18:21:56 -070014unsigned long lpj_fine;
Randy Dunlapbfe8df32007-10-16 01:23:46 -070015unsigned long preset_lpj;
Linus Torvalds1da177e2005-04-16 15:20:36 -070016static int __init lpj_setup(char *str)
17{
18 preset_lpj = simple_strtoul(str,NULL,0);
19 return 1;
20}
21
22__setup("lpj=", lpj_setup);
23
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070024#ifdef ARCH_HAS_READ_CURRENT_TIMER
25
26/* This routine uses the read_current_timer() routine and gets the
27 * loops per jiffy directly, instead of guessing it using delay().
28 * Also, this code tries to handle non-maskable asynchronous events
29 * (like SMIs)
30 */
31#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
32#define MAX_DIRECT_CALIBRATION_RETRIES 5
33
Adrian Bunk6c81c322008-02-06 01:37:51 -080034static unsigned long __cpuinit calibrate_delay_direct(void)
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070035{
36 unsigned long pre_start, start, post_start;
37 unsigned long pre_end, end, post_end;
38 unsigned long start_jiffies;
Alok Katariaf3f31492008-06-23 18:21:56 -070039 unsigned long timer_rate_min, timer_rate_max;
40 unsigned long good_timer_sum = 0;
41 unsigned long good_timer_count = 0;
Andrew Worsleyd2b46312011-05-24 17:13:15 -070042 unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
43 int max = -1; /* index of measured_times with max/min values or not set */
44 int min = -1;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070045 int i;
46
47 if (read_current_timer(&pre_start) < 0 )
48 return 0;
49
50 /*
51 * A simple loop like
52 * while ( jiffies < start_jiffies+1)
53 * start = read_current_timer();
54 * will not do. As we don't really know whether jiffy switch
55 * happened first or timer_value was read first. And some asynchronous
56 * event can happen between these two events introducing errors in lpj.
57 *
58 * So, we do
59 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
60 * 2. check jiffy switch
61 * 3. start <- timer value before or after jiffy switch
62 * 4. post_start <- When we are sure that jiffy switch has happened
63 *
64 * Note, we don't know anything about order of 2 and 3.
65 * Now, by looking at post_start and pre_start difference, we can
66 * check whether any asynchronous event happened or not
67 */
68
69 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
70 pre_start = 0;
71 read_current_timer(&start);
72 start_jiffies = jiffies;
Tim Deegan70a06222011-02-10 08:50:41 +000073 while (time_before_eq(jiffies, start_jiffies + 1)) {
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070074 pre_start = start;
75 read_current_timer(&start);
76 }
77 read_current_timer(&post_start);
78
79 pre_end = 0;
80 end = post_start;
Tim Deegan70a06222011-02-10 08:50:41 +000081 while (time_before_eq(jiffies, start_jiffies + 1 +
82 DELAY_CALIBRATION_TICKS)) {
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070083 pre_end = end;
84 read_current_timer(&end);
85 }
86 read_current_timer(&post_end);
87
Alok Katariaf3f31492008-06-23 18:21:56 -070088 timer_rate_max = (post_end - pre_start) /
89 DELAY_CALIBRATION_TICKS;
90 timer_rate_min = (pre_end - post_start) /
91 DELAY_CALIBRATION_TICKS;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070092
93 /*
Alok Katariaf3f31492008-06-23 18:21:56 -070094 * If the upper limit and lower limit of the timer_rate is
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070095 * >= 12.5% apart, redo calibration.
96 */
Andrew Worsleyd2b46312011-05-24 17:13:15 -070097 if (start >= post_end)
98 printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
99 "timer_rate as we had a TSC wrap around"
100 " start=%lu >=post_end=%lu\n",
101 start, post_end);
102 if (start < post_end && pre_start != 0 && pre_end != 0 &&
Alok Katariaf3f31492008-06-23 18:21:56 -0700103 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
104 good_timer_count++;
105 good_timer_sum += timer_rate_max;
Andrew Worsleyd2b46312011-05-24 17:13:15 -0700106 measured_times[i] = timer_rate_max;
107 if (max < 0 || timer_rate_max > measured_times[max])
108 max = i;
109 if (min < 0 || timer_rate_max < measured_times[min])
110 min = i;
111 } else
112 measured_times[i] = 0;
113
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700114 }
115
Andrew Worsleyd2b46312011-05-24 17:13:15 -0700116 /*
117 * Find the maximum & minimum - if they differ too much throw out the
118 * one with the largest difference from the mean and try again...
119 */
120 while (good_timer_count > 1) {
121 unsigned long estimate;
122 unsigned long maxdiff;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700123
Andrew Worsleyd2b46312011-05-24 17:13:15 -0700124 /* compute the estimate */
125 estimate = (good_timer_sum/good_timer_count);
126 maxdiff = estimate >> 3;
127
128 /* if range is within 12% let's take it */
129 if ((measured_times[max] - measured_times[min]) < maxdiff)
130 return estimate;
131
132 /* ok - drop the worse value and try again... */
133 good_timer_sum = 0;
134 good_timer_count = 0;
135 if ((measured_times[max] - estimate) <
136 (estimate - measured_times[min])) {
137 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
138 "min bogoMips estimate %d = %lu\n",
139 min, measured_times[min]);
140 measured_times[min] = 0;
141 min = max;
142 } else {
143 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
144 "max bogoMips estimate %d = %lu\n",
145 max, measured_times[max]);
146 measured_times[max] = 0;
147 max = min;
148 }
149
150 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
151 if (measured_times[i] == 0)
152 continue;
153 good_timer_count++;
154 good_timer_sum += measured_times[i];
155 if (measured_times[i] < measured_times[min])
156 min = i;
157 if (measured_times[i] > measured_times[max])
158 max = i;
159 }
160
161 }
162
163 printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
164 "estimate for loops_per_jiffy.\nProbably due to long platform "
165 "interrupts. Consider using \"lpj=\" boot option.\n");
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700166 return 0;
167}
168#else
Adrian Bunk6c81c322008-02-06 01:37:51 -0800169static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700170#endif
171
Linus Torvalds1da177e2005-04-16 15:20:36 -0700172/*
173 * This is the number of bits of precision for the loops_per_jiffy. Each
Phil Carmody191e5682011-03-22 16:34:13 -0700174 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
175 * to start with a good estimate.
Alok Kataria3da757d2008-06-20 15:06:33 -0700176 * For the boot cpu we can skip the delay calibration and assign it a value
Alok Katariaf3f31492008-06-23 18:21:56 -0700177 * calculated based on the timer frequency.
178 * For the rest of the CPUs we cannot assume that the timer frequency is same as
Alok Kataria3da757d2008-06-20 15:06:33 -0700179 * the cpu frequency, hence do the calibration for those.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700180 */
181#define LPS_PREC 8
182
Phil Carmody71c696b2011-03-22 16:34:12 -0700183static unsigned long __cpuinit calibrate_delay_converge(void)
184{
Phil Carmody191e5682011-03-22 16:34:13 -0700185 /* First stage - slowly accelerate to find initial bounds */
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700186 unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
Phil Carmody191e5682011-03-22 16:34:13 -0700187 int trials = 0, band = 0, trial_in_band = 0;
Phil Carmody71c696b2011-03-22 16:34:12 -0700188
189 lpj = (1<<12);
Phil Carmody191e5682011-03-22 16:34:13 -0700190
191 /* wait for "start of" clock tick */
192 ticks = jiffies;
193 while (ticks == jiffies)
194 ; /* nothing */
195 /* Go .. */
196 ticks = jiffies;
197 do {
198 if (++trial_in_band == (1<<band)) {
199 ++band;
200 trial_in_band = 0;
201 }
202 __delay(lpj * band);
203 trials += band;
204 } while (ticks == jiffies);
205 /*
206 * We overshot, so retreat to a clear underestimate. Then estimate
207 * the largest likely undershoot. This defines our chop bounds.
208 */
209 trials -= band;
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700210 loopadd_base = lpj * band;
211 lpj_base = lpj * trials;
212
213recalibrate:
214 lpj = lpj_base;
215 loopadd = loopadd_base;
Phil Carmody71c696b2011-03-22 16:34:12 -0700216
217 /*
218 * Do a binary approximation to get lpj set to
Phil Carmody191e5682011-03-22 16:34:13 -0700219 * equal one clock (up to LPS_PREC bits)
Phil Carmody71c696b2011-03-22 16:34:12 -0700220 */
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700221 chop_limit = lpj >> LPS_PREC;
Phil Carmody191e5682011-03-22 16:34:13 -0700222 while (loopadd > chop_limit) {
223 lpj += loopadd;
Phil Carmody71c696b2011-03-22 16:34:12 -0700224 ticks = jiffies;
225 while (ticks == jiffies)
Phil Carmody191e5682011-03-22 16:34:13 -0700226 ; /* nothing */
Phil Carmody71c696b2011-03-22 16:34:12 -0700227 ticks = jiffies;
228 __delay(lpj);
229 if (jiffies != ticks) /* longer than 1 tick */
Phil Carmody191e5682011-03-22 16:34:13 -0700230 lpj -= loopadd;
231 loopadd >>= 1;
Phil Carmody71c696b2011-03-22 16:34:12 -0700232 }
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700233 /*
234 * If we incremented every single time possible, presume we've
235 * massively underestimated initially, and retry with a higher
236 * start, and larger range. (Only seen on x86_64, due to SMIs)
237 */
238 if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
239 lpj_base = lpj;
240 loopadd_base <<= 2;
241 goto recalibrate;
242 }
Phil Carmody71c696b2011-03-22 16:34:12 -0700243
244 return lpj;
245}
246
Sameer Nanda7afe1842011-07-25 17:13:29 -0700247static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
248
Adrian Bunk6c81c322008-02-06 01:37:51 -0800249void __cpuinit calibrate_delay(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700250{
Russell King1b19ca92011-06-22 11:55:50 +0100251 unsigned long lpj;
Mike Travisfeae3202009-11-17 18:22:13 -0600252 static bool printed;
Sameer Nanda7afe1842011-07-25 17:13:29 -0700253 int this_cpu = smp_processor_id();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700254
Sameer Nanda7afe1842011-07-25 17:13:29 -0700255 if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
256 lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
257 pr_info("Calibrating delay loop (skipped) "
258 "already calibrated this CPU");
259 } else if (preset_lpj) {
Russell King1b19ca92011-06-22 11:55:50 +0100260 lpj = preset_lpj;
Mike Travisfeae3202009-11-17 18:22:13 -0600261 if (!printed)
262 pr_info("Calibrating delay loop (skipped) "
263 "preset value.. ");
264 } else if ((!printed) && lpj_fine) {
Russell King1b19ca92011-06-22 11:55:50 +0100265 lpj = lpj_fine;
Mike Travisfeae3202009-11-17 18:22:13 -0600266 pr_info("Calibrating delay loop (skipped), "
Alok Katariaf3f31492008-06-23 18:21:56 -0700267 "value calculated using timer frequency.. ");
Russell King1b19ca92011-06-22 11:55:50 +0100268 } else if ((lpj = calibrate_delay_direct()) != 0) {
Mike Travisfeae3202009-11-17 18:22:13 -0600269 if (!printed)
270 pr_info("Calibrating delay using timer "
271 "specific routine.. ");
Linus Torvalds1da177e2005-04-16 15:20:36 -0700272 } else {
Mike Travisfeae3202009-11-17 18:22:13 -0600273 if (!printed)
274 pr_info("Calibrating delay loop... ");
Russell King1b19ca92011-06-22 11:55:50 +0100275 lpj = calibrate_delay_converge();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700276 }
Sameer Nanda7afe1842011-07-25 17:13:29 -0700277 per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
Mike Travisfeae3202009-11-17 18:22:13 -0600278 if (!printed)
279 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
Russell King1b19ca92011-06-22 11:55:50 +0100280 lpj/(500000/HZ),
281 (lpj/(5000/HZ)) % 100, lpj);
Mike Travisfeae3202009-11-17 18:22:13 -0600282
Russell King1b19ca92011-06-22 11:55:50 +0100283 loops_per_jiffy = lpj;
Mike Travisfeae3202009-11-17 18:22:13 -0600284 printed = true;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700285}