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

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Message-ID: <20171222121445.GB30968@e110439-lin>
Date:   Fri, 22 Dec 2017 12:14:45 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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 13:07, Juri Lelli wrote:
> Hi Peter,
> 
> On 22/12/17 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.
> > 
> > > 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;
> > but I suppose there's nothing stopping anybody from splitting a clock
> > domain down the middle scheduling wise. So yes, good point.
> 
> Also, for CFS current behaviour is to start ignoring contributions after
> TICK_NS. It seems that your change might introduce regressions?

Good point, an energy regression I guess you mean...

I think that check is already gone for CFS in the current PeterZ tree.
It seems we use TICK_NS just for the reset of iowait_boost, isn't it?

However, if the remote updates of CFS works as expected,
the removal of the TICK_NS for CFS is not intentional?

-- 
#include <best/regards.h>

Patrick Bellasi