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sched: Do not account bogus utime

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Due to rounding in scale_stime(), for big numbers, scaled stime
values will grow in chunks. Since rtime grow in jiffies and we
calculate utime like below:

	prev->stime = max(prev->stime, stime);
	prev->utime = max(prev->utime, rtime - prev->stime);

we could erroneously account stime values as utime. To prevent
that only update prev->{u,s}time values when they are smaller
than current rtime.

Signed-off-by: Stanislaw Gruszka <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Stanislaw Gruszka 2013-04-30 11:35:05 +02:00 • committed by Ingo Molnar
commit 772c808a25
1 changed files with 9 additions and 0 deletions
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9
kernel/sched/cputime.c
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@ -581,6 +581,14 @@ static void cputime_adjust(struct task_cputime *curr,
*/
rtime = nsecs_to_cputime(curr->sum_exec_runtime);
/*
* Update userspace visible utime/stime values only if actual execution
* time is bigger than already exported. Note that can happen, that we
* provided bigger values due to scaling inaccuracy on big numbers.
*/
if (prev->stime + prev->utime >= rtime)
goto out;
if (!rtime) {
stime = 0;
} else if (!total) {
@ -598,6 +606,7 @@ static void cputime_adjust(struct task_cputime *curr,
prev->stime = max(prev->stime, stime);
prev->utime = max(prev->utime, rtime - prev->stime);
out:
*ut = prev->utime;
*st = prev->stime;
}