| From 772c808a252594692972773f6ee41c289b8e0b2a Mon Sep 17 00:00:00 2001 |
| From: Stanislaw Gruszka <sgruszka@redhat.com> |
| Date: Tue, 30 Apr 2013 11:35:05 +0200 |
| Subject: sched: Do not account bogus utime |
| |
| From: Stanislaw Gruszka <sgruszka@redhat.com> |
| |
| commit 772c808a252594692972773f6ee41c289b8e0b2a upstream. |
| |
| 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 <sgruszka@redhat.com> |
| Cc: Frederic Weisbecker <fweisbec@gmail.com> |
| Cc: rostedt@goodmis.org |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Dave Hansen <dave@sr71.net> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@redhat.com |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/sched/cputime.c | 9 +++++++++ |
| 1 file changed, 9 insertions(+) |
| |
| --- a/kernel/sched/cputime.c |
| +++ b/kernel/sched/cputime.c |
| @@ -591,6 +591,14 @@ static void cputime_adjust(struct task_c |
| */ |
| 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) { |
| @@ -608,6 +616,7 @@ static void cputime_adjust(struct task_c |
| prev->stime = max(prev->stime, stime); |
| prev->utime = max(prev->utime, rtime - prev->stime); |
| |
| +out: |
| *ut = prev->utime; |
| *st = prev->stime; |
| } |