From 772c808a252594692972773f6ee41c289b8e0b2a Mon Sep 17 00:00:00 2001 From: Stanislaw Gruszka Date: Tue, 30 Apr 2013 11:35:05 +0200 Subject: [PATCH] sched: Do not account bogus utime 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 Cc: Frederic Weisbecker Cc: rostedt@goodmis.org Cc: Linus Torvalds Cc: Dave Hansen Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar --- kernel/sched/cputime.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index e9198ab..1b7c216 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -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; } -- 2.7.4