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authorPeter Zijlstra <peterz@infradead.org>2016-08-15 18:38:42 +0200
committerIngo Molnar <mingo@kernel.org>2016-08-18 10:48:46 +0200
commit173be9a14f7b2e901cf77c18b1aafd4d672e9d9e (patch)
treed90bbe487b1aa4ca149b68e7323b3e2ac2940c6d
parent3684b03d8e9a889eda94ee74421959a9d55e5e19 (diff)
sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression
Mike reports: Roughly 10% of the time, ltp testcase getrusage04 fails: getrusage04 0 TINFO : Expected timers granularity is 4000 us getrusage04 0 TINFO : Using 1 as multiply factor for max [us]time increment (1000+4000us)! getrusage04 0 TINFO : utime: 0us; stime: 179us getrusage04 0 TINFO : utime: 3751us; stime: 0us getrusage04 1 TFAIL : getrusage04.c:133: stime increased > 5000us: And tracked it down to the case where the task simply doesn't get _any_ [us]time ticks. Update the code to assume all rtime is utime when we lack information, thus ensuring a task that elides the tick gets time accounted. Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com> Tested-by: Mike Galbraith <umgwanakikbuti@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Fredrik Markstrom <fredrik.markstrom@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Radim <rkrcmar@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vince Weaver <vincent.weaver@maine.edu> Cc: Wanpeng Li <wanpeng.li@hotmail.com> Cc: stable@vger.kernel.org # 4.3+ Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime") Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/sched/cputime.c15
1 files changed, 10 insertions, 5 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 9858266fb0b3..2ee83b200504 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -614,19 +614,25 @@ static void cputime_adjust(struct task_cputime *curr,
stime = curr->stime;
utime = curr->utime;
- if (utime == 0) {
- stime = rtime;
+ /*
+ * If either stime or both stime and utime are 0, assume all runtime is
+ * userspace. Once a task gets some ticks, the monotonicy code at
+ * 'update' will ensure things converge to the observed ratio.
+ */
+ if (stime == 0) {
+ utime = rtime;
goto update;
}
- if (stime == 0) {
- utime = rtime;
+ if (utime == 0) {
+ stime = rtime;
goto update;
}
stime = scale_stime((__force u64)stime, (__force u64)rtime,
(__force u64)(stime + utime));
+update:
/*
* Make sure stime doesn't go backwards; this preserves monotonicity
* for utime because rtime is monotonic.
@@ -649,7 +655,6 @@ static void cputime_adjust(struct task_cputime *curr,
stime = rtime - utime;
}
-update:
prev->stime = stime;
prev->utime = utime;
out: