linux-kernel - Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates

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Date:   Fri, 22 Dec 2017 12:07:37 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates

On 22-Dec 12:46, Peter Zijlstra wrote:
> On Fri, Dec 22, 2017 at 11:02:06AM +0000, Patrick Bellasi wrote:
> > > @@ -315,8 +315,8 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
> > >  		unsigned long j_util, j_max;
> > >  		s64 delta_ns;
> > >  
> > > -		if (j_sg_cpu != sg_cpu)
> > > -			sugov_get_util(j_sg_cpu);
> > > +		if (idle_cpu(j))
> > > +			continue;
> > 
> > That should work to skip IDLE CPUs... however I'm missing where now we
> > get the sugov_get_util(j_sg_cpu) for active CPUs. It has been moved
> > somewhere else I guess...
> 
> No, I'm just an idiot... lemme fix that.

Then you just missed a call to sugov_get_util(j_sg_cpu) after the
above if... right, actually that was Viresh proposal...

> > Moreover, that way don't we completely disregard CFS blocked load for
> > IDLE CPUs... as well as DL reserved utilization, which should be
> > released only at the 0-lag time?
> 
> I was thinking that since dl is a 'global' scheduler the reservation
> would be too and thus the freq just needs a single CPU to be observed;

AFAIU global is only the admission control (which is something worth a
thread by itself...) while the dl_se->dl_bw are aggregated into the
dl_rq->running_bw, which ultimately represents the DL bandwidth
required for just a CPU.

> but I suppose there's nothing stopping anybody from splitting a clock
> domain down the middle scheduling wise. So yes, good point.

That makes sense... moreover, using the global utilization, we would
end up asking for capacities which cannot be provided by a single CPU.

> Blergh that'd make a mess of things again.

Actually, looking better at your patch: are we not just ok with that?

I mean, we don't need this check on idle_cpu since in
sugov_aggregate_util we already skip the util=sg_cpu->max in case of
!rq->rt.rt_nr_running, while we aggregate just CFS and DL requests.

-- 
#include <best/regards.h>

Patrick Bellasi