linux-kernel - Re: [PATCH 10/39] sched: Factor out update_other_load_avgs() from __update_blocked

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Date: Tue, 25 Jun 2024 11:13:54 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Tejun Heo <tj@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, torvalds@...ux-foundation.org, mingo@...hat.com, 
	juri.lelli@...hat.com, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, 
	ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	martin.lau@...nel.org, joshdon@...gle.com, brho@...gle.com, pjt@...gle.com, 
	derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com, 
	dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com, 
	changwoo@...lia.com, himadrics@...ia.fr, memxor@...il.com, 
	andrea.righi@...onical.com, joel@...lfernandes.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 10/39] sched: Factor out update_other_load_avgs() from __update_blocked_others()

On Mon, 24 Jun 2024 at 21:24, Tejun Heo <tj@...nel.org> wrote:
>
> Hello, Peter, Vincent.
>
> On Mon, Jun 24, 2024 at 06:15:20PM +0200, Vincent Guittot wrote:
> > > > +bool update_other_load_avgs(struct rq *rq)
> > > > +{
> > > > +     u64 now = rq_clock_pelt(rq);
> > > > +     const struct sched_class *curr_class = rq->curr->sched_class;
> > > > +     unsigned long thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
> > > > +
> > > > +     lockdep_assert_rq_held(rq);
> > > > +
> > > > +     return update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
> > > > +             update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
> > > > +             update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure) |
> > > > +             update_irq_load_avg(rq, 0);
> > > > +}
> > >
> > > Yeah, but you then ignore the return value and don't call into cpufreq.
> > >
> > > Vincent, what would be the right thing to do here?
> >
> > These metrics are only consumed by fair class so my first question would be:
> >
> > - Do we plan to have a fair and sched_ext to coexist ? Or is it
> > exclusive ? I haven't been able to get a clear answer on this while
> > reading the cover letter
>
> Oh, there are two modes. In partial mode (SCX_OPS_SWITCH_PARTIAL), there can
> be both CFS and SCX tasks running on the same system. If the flag is not
> set, the whole system is on SCX.

ok thanks for the clarification because this will have an impact on
how fair tasks are scheduled

>
> > - If sched_ext is exclusive to fair then I'm not sure that you need to
> > update them at all because they will not be used. RT uses a  fix freq
> > and DL use the Sum of running DL bandwidth. But if both an coexist we
> > use be sure to update them periodically
>
> Hmm.... I think I saw RT's schedutil signal stuck high constantly pushing up
> the frequency. I might be mistaken tho. I'll check again.

This is used when selecting a frequency for fair tasks

>
> Thanks.

>
> --
> tejun