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| Started by | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| First post | 2016-08-10 20:40 +0200 |
| Last post | 2016-08-10 20:40 +0200 |
| Articles | 1 — 1 participant |
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Re: [patch] sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression Peter Zijlstra <peterz@infradead.org> - 2016-08-10 20:40 +0200
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2016-08-10 20:40 +0200 |
| Subject | Re: [patch] sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression |
| Message-ID | <s4Gqm-b4-29@gated-at.bofh.it> |
On Wed, Aug 10, 2016 at 02:30:33PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 10, 2016 at 01:14:29PM +0200, Mike Galbraith wrote:
> > Hi Peter,
> >
> > While running ltp, the fates decided it was time for me to encounter
> > the roughly 1 out of every 10 call failure below. As much as I run
> > ltp, I'm a bit surprised that I (or anyone else) haven't met this
> > before, but then the fates are known to be a tad fickle.
> >
> > 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:
> >
> > When applying the full rtime to either stime or utime, do not overwrite
> > the previously tallied value.
> >
> > Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime")
> > Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
> > Cc: stable@vger.kernel.org # 4.3+
> > ---
> > kernel/sched/cputime.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > --- a/kernel/sched/cputime.c
> > +++ b/kernel/sched/cputime.c
> > @@ -608,11 +608,13 @@ static void cputime_adjust(struct task_c
> >
> > if (utime == 0) {
> > stime = rtime;
> > + utime = prev->utime;
> > goto update;
> > }
> >
> > if (stime == 0) {
> > utime = rtime;
> > + stime = prev->stime;
> > goto update;
> > }
>
> This cannot be right; it violates that utime+stime==rtime. Let me try
> and figure out what actually happens.
Any idea where your [us]time are coming from? Do you end up in the
vtime_accounting_enabled() path or not?
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