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authorStanislaw Gruszka <sgruszka@redhat.com>2013-04-30 11:35:05 +0200
committerIngo Molnar <mingo@kernel.org>2013-04-30 19:13:04 +0200
commit772c808a252594692972773f6ee41c289b8e0b2a (patch)
tree1c1c2631ca1133df1bfe0c5a47d2d49dfe864895 /kernel/sched
parent55eaa7c1f511af5fb6ef808b5328804f4d4e5243 (diff)
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@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>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/cputime.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index e9198abfca5..1b7c2161f5c 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;
}