4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra <pet...@infradead.org>
commit 173be9a14f7b2e901cf77c18b1aafd4d672e9d9e upstream.
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 <umgwanakikb...@gmail.com>
Tested-by: Mike Galbraith <umgwanakikb...@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Fredrik Markstrom <fredrik.markst...@gmail.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Radim <rkrc...@redhat.com>
Cc: Rik van Riel <r...@redhat.com>
Cc: Stephane Eranian <eran...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Vince Weaver <vincent.wea...@maine.edu>
Cc: Wanpeng Li <wanpeng...@hotmail.com>
Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime")
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
kernel/sched/cputime.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -600,19 +600,25 @@ static void cputime_adjust(struct task_c
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.
@@ -635,7 +641,6 @@ static void cputime_adjust(struct task_c
stime = rtime - utime;
}
-update:
prev->stime = stime;
prev->utime = utime;
out:
