softlockup: remove timestamp checking from hung_task
Impact: saves sizeof(long) bytes per task_struct
By guaranteeing that sysctl_hung_task_timeout_secs have elapsed between
tasklist scans we can avoid using timestamps.
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 3951a80..0c924de 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -34,7 +34,6 @@
* Zero means infinite timeout - no checking done:
*/
unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
-static unsigned long __read_mostly hung_task_poll_jiffies;
unsigned long __read_mostly sysctl_hung_task_warnings = 10;
@@ -69,33 +68,17 @@
.notifier_call = hung_task_panic,
};
-/*
- * Returns seconds, approximately. We don't need nanosecond
- * resolution, and we don't need to waste time with a big divide when
- * 2^30ns == 1.074s.
- */
-static unsigned long get_timestamp(void)
-{
- int this_cpu = raw_smp_processor_id();
-
- return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
-}
-
-static void check_hung_task(struct task_struct *t, unsigned long now,
- unsigned long timeout)
+static void check_hung_task(struct task_struct *t, unsigned long timeout)
{
unsigned long switch_count = t->nvcsw + t->nivcsw;
if (t->flags & PF_FROZEN)
return;
- if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
+ if (switch_count != t->last_switch_count) {
t->last_switch_count = switch_count;
- t->last_switch_timestamp = now;
return;
}
- if ((long)(now - t->last_switch_timestamp) < timeout)
- return;
if (!sysctl_hung_task_warnings)
return;
sysctl_hung_task_warnings--;
@@ -111,7 +94,6 @@
sched_show_task(t);
__debug_show_held_locks(t);
- t->last_switch_timestamp = now;
touch_nmi_watchdog();
if (sysctl_hung_task_panic)
@@ -145,7 +127,6 @@
{
int max_count = sysctl_hung_task_check_count;
int batch_count = HUNG_TASK_BATCHING;
- unsigned long now = get_timestamp();
struct task_struct *g, *t;
/*
@@ -168,19 +149,16 @@
}
/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
if (t->state == TASK_UNINTERRUPTIBLE)
- check_hung_task(t, now, timeout);
+ check_hung_task(t, timeout);
} while_each_thread(g, t);
unlock:
rcu_read_unlock();
}
-static void update_poll_jiffies(void)
+static unsigned long timeout_jiffies(unsigned long timeout)
{
/* timeout of 0 will disable the watchdog */
- if (sysctl_hung_task_timeout_secs == 0)
- hung_task_poll_jiffies = MAX_SCHEDULE_TIMEOUT;
- else
- hung_task_poll_jiffies = sysctl_hung_task_timeout_secs * HZ / 2;
+ return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
}
/*
@@ -197,8 +175,6 @@
if (ret || !write)
goto out;
- update_poll_jiffies();
-
wake_up_process(watchdog_task);
out:
@@ -211,20 +187,14 @@
static int watchdog(void *dummy)
{
set_user_nice(current, 0);
- update_poll_jiffies();
for ( ; ; ) {
- unsigned long timeout;
+ unsigned long timeout = sysctl_hung_task_timeout_secs;
- while (schedule_timeout_interruptible(hung_task_poll_jiffies));
+ while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
+ timeout = sysctl_hung_task_timeout_secs;
- /*
- * Need to cache timeout here to avoid timeout being set
- * to 0 via sysctl while inside check_hung_*_tasks().
- */
- timeout = sysctl_hung_task_timeout_secs;
- if (timeout)
- check_hung_uninterruptible_tasks(timeout);
+ check_hung_uninterruptible_tasks(timeout);
}
return 0;