Re: [PATCH v3] sched: Don't try to catch up excess steal time.

[Joel Fernandes]

On Tue, Nov 19, 2024 at 9:17 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Tue, 19 Nov 2024 09:10:41 +0900
> Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
>
> > > > +++ b/kernel/sched/core.c
> > > > @@ -766,13 +766,15 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
> > > >  #endif
> > > >  #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
> > > >       if (static_key_false((&paravirt_steal_rq_enabled))) {
> > > > -             steal = paravirt_steal_clock(cpu_of(rq));
> > > > +             u64 prev_steal;
> > > > +
> > > > +             steal = prev_steal = paravirt_steal_clock(cpu_of(rq));
> > > >               steal -= rq->prev_steal_time_rq;
> > > >
> > > >               if (unlikely(steal > delta))
> > > >                       steal = delta;
> > >
> > > So is the problem just the above if statement? That is, delta is already
> > > calculated, but if we get interrupted by the host before steal is
> > > calculated and the time then becomes greater than delta, the time
> > > difference between delta and steal gets pushed off to the next task, right?
> >
> > Pretty much.. the steal being capped to delta means the rest of the
> > steal is pushed off to the future. Instead he discards the remaining
> > steal after this patch.
>
> Thanks for confirming. I just wanted to make sure I understand as the
> initial change log went into a lot of detail where I sorta got lost ;-)

No problem!! Glad we're on the same page about the change.

thanks,

 - Joel