Commit-ID: 772c808a252594692972773f6ee41c289b8e0b2a
Gitweb: http://git.kernel.org/tip/772c808a252594692972773f6ee41c289b8e0b2a
Author: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
AuthorDate: Tue, 30 Apr 2013 11:35:05 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 30 Apr 2013 19:13:04 +0200
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 <sgruszka@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: rostedt@xxxxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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;
}
--
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