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sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression

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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 <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>
Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Zijlstra 2016-08-15 18:38:42 +02:00 committed by Greg Kroah-Hartman
parent 51ed10c4ff
commit c3cf68ec55
1 changed files with 10 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
kernel/sched/cputime.c
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@ -600,19 +600,25 @@ 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.
@ -635,7 +641,6 @@ static void cputime_adjust(struct task_cputime *curr,
stime = rtime - utime;
}
update:
prev->stime = stime;
prev->utime = utime;
out: