linux-kernel - Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

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Message-ID: <20180622132953.GM2494@hirez.programming.kicks-ass.net>
Date:   Fri, 22 Jun 2018 15:29:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, rjw@...ysocki.net,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        Morten.Rasmussen@....com, viresh.kumar@...aro.org,
        valentin.schneider@....com, patrick.bellasi@....com,
        joel@...lfernandes.org, daniel.lezcano@...aro.org,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

On Fri, Jun 22, 2018 at 01:54:34PM +0100, Quentin Perret wrote:
> On Friday 22 Jun 2018 at 13:37:13 (+0200), Peter Zijlstra wrote:
> > That is true.. So we could limit the scaling to the case where there is
> > no idle time, something like:
> > 
> > 	util = sg_cpu->util_cfs;
> > 
> > 	cap_cfs = (1024 - (sg_cpu->util_rt + ...));
> > 	if (util == cap_cfs)
> > 		util = sg_cpu->max;
> > 
> > That specifically handles the '0% idle -> 100% freq' case, but I don't
> > realy like edge behaviour like that. If for some reason it all doesn't
> > quite align you're left with bits.
> > 
> > And the linear scaling is the next simplest thing that avoids the hard
> > boundary case.
> 
> Right, so maybe we'll get something smoother by just summing the signals
> as Vincent is proposing ? 

Sure, but see my previous mail just now, that has the problem of
u_{rt,dl} distoting f_{rt,dl} even when there is no u_cfs.