On (09/03/13 10:43), Stanislaw Gruszka wrote:
> > > > Thanks a lot Sergey for testing this further!
> > > >
> > > > Interesting results, so rtime is always one or two units off stime
> > > > after scaling.
> > > > Stanislaw made the scaling code with Linus and he has a better idea on
> > > > the math guts
> > > > here.
> > >
> > > I don't think this is scale issue, but rather at scale_stime() input
> > > stime is already bigger then rtime. Sergey, could you verify that
> > > by adding check before scale_stime() ?
> > >
> >
> > usually stime < rtime.
> > this is what scale_stime() gets as input:
> >
> > [ 1291.409566] stime:3790580815 rtime:4344293130 total:3790580815
>
> Ok, I see now, utime is 0 . This seems to be problem with dynamic ticks
> as you told that your application is kernel compilation, so we utilize
> lot of cpu time in user-space.
>
> Anyway we should handle utime == 0 situation on scaling code. We work
> well when rtime & stime are not big (variables and results fit in
> 32 bit), otherwise we have that stime bigger than rtime problem. Let's
> try to handle the problem by below patch. Sergey, does it work for you ?
works fine on -next.
-ss
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index a7959e0..25cc35d 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -557,7 +557,7 @@ static void cputime_adjust(struct task_cputime *curr,
> struct cputime *prev,
> cputime_t *ut, cputime_t *st)
> {
> - cputime_t rtime, stime, utime, total;
> + cputime_t rtime, stime, utime;
>
> if (vtime_accounting_enabled()) {
> *ut = curr->utime;
> @@ -565,9 +565,6 @@ static void cputime_adjust(struct task_cputime *curr,
> return;
> }
>
> - stime = curr->stime;
> - total = stime + curr->utime;
> -
> /*
> * Tick based cputime accounting depend on random scheduling
> * timeslices of a task to be interrupted or not by the timer.
> @@ -588,13 +585,19 @@ static void cputime_adjust(struct task_cputime *curr,
> if (prev->stime + prev->utime >= rtime)
> goto out;
>
> - if (total) {
> + stime = curr->stime;
> + utime = curr->utime;
> +
> + if (utime == 0) {
> + stime = rtime;
> + } else if (stime == 0) {
> + utime = rtime;
> + } else {
> + cputime_t total = stime + utime;
> +
> stime = scale_stime((__force u64)stime,
> (__force u64)rtime, (__force u64)total);
> utime = rtime - stime;
> - } else {
> - stime = rtime;
> - utime = 0;
> }
>
> /*
>
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