On (09/02/13 16:13), Frederic Weisbecker wrote:
> > On Mon, Sep 02, 2013 at 03:07:45PM +0200, Frederic Weisbecker wrote:
> > > > Hope this may help.
> > > > I've added a silly check to make sure that `stime < rtime'
> > > >
> > > > @@ -579,6 +582,10 @@ static void cputime_adjust(struct task_cputime
> > > > *curr,
> > > > if (total) {
> > > > stime = scale_stime((__force u64)stime,
> > > > (__force u64)rtime, (__force
> > > > u64)total);
> > > > + if (stime > rtime) {
> > > > + printk(KERN_ERR "Ooops: stime:%llu
> > > > rtime:%llu\n", stime, rtime);
> > > > + WARN_ON(1);
> > > > + }
> > > > utime = rtime - stime;
> > > > } else {
> > > > stime = rtime;
> > [snip]
> >
> > > 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() ?
>
> Note that having stime > rtime should be fine to handle. This can happen for
> example if the task runs on tiny timeslices but is unlucky enough that all
> these
> timeslices are interrupted by the tick.
>
even is stime > rtime, scale_stime() fixes it:
if (stime > rtime)
swap(rtime, stime);
-ss
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