linux-kernel - Re: [PATCH 2/2] sched: cpufreq: use rt_avg as estimate of required RT CPU capacity

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Message-ID: <20160902093549.GU9337@e106622-lin>
Date:   Fri, 2 Sep 2016 10:35:49 +0100
From:   Juri Lelli <Juri.Lelli@....com>
To:     Steve Muckle <steve.muckle@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH 2/2] sched: cpufreq: use rt_avg as estimate of required
 RT CPU capacity

On 01/09/16 14:48, Steve Muckle wrote:
> On Wed, Aug 31, 2016 at 06:00:02PM +0100, Juri Lelli wrote:
> > > Another problem is that we have many semi related knobs; we have the
> > > global RT runtime limit knob, but that doesn't affect cpufreq (maybe it
> > > should)
> > 
> > Maybe we could create this sort of link when using the cgroup RT
> > throttling interface as well? It should still then fit well once we
> > replace the underlying mechanism with DL reservations. And, AFAIK, the
> > interface is used by Android folks already.
> 
> I'm not sure how the upper bounds can be used to infer CPU frequency...
> On my Nexus 6p (an Android device), the global RT runtime limit
> seems to be set at 950ms/1sec, the root cgroup is set to 800ms/1sec, and
> bg_non_interactive is set at 700ms/1sec.
> 

Right, unfortunately. Still too coarse grained (as Thomas is also saying
in his last reply, if I read it correctly). Doesn't pay off the added
complexity I'm afraid.