Date: Thu, 30 Mar 2017 09:58:05 +0100
From: Juri Lelli <juri.lelli@arm.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: peterz@infradead.org, mingo@redhat.com, viresh.kumar@linaro.org,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        tglx@linutronix.de, vincent.guittot@linaro.org, rostedt@goodmis.org,
        luca.abeni@santannapisa.it, claudio@evidence.eu.com,
        tommaso.cucinotta@santannapisa.it, bristot@redhat.com,
        mathieu.poirier@linaro.org, tkjos@android.com, joelaf@google.com,
        andresoportus@google.com, morten.rasmussen@arm.com,
        dietmar.eggemann@arm.com, patrick.bellasi@arm.com,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFD PATCH 4/5] sched/cpufreq_schedutil: always consider all
 CPUs when deciding next freq
Message-ID: <20170330085805.GF18960@e106622-lin>
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Hi,

On 30/03/17 00:41, Rafael J. Wysocki wrote:
> On Friday, March 24, 2017 02:08:59 PM Juri Lelli wrote:
> > No assumption can be made upon the rate at which frequency updates get
> > triggered, as there are scheduling policies (like SCHED_DEADLINE) which
> > don't trigger them so frequently.
> > 
> > Remove such assumption from the code.
> 
> But the util/max values for idle CPUs may be stale, no?
> 

Right, that might be a problem. A proper solution I think would be to
remotely update such values for idle CPUs, and I believe Vincent is
working on a patch for that.

As mid-term workarounds, changing a bit the current one, come to my
mind:

 - consider TICK_NSEC (continue) only when SCHED_CPUFREQ_DL is not set
 - remove CFS contribution (without triggering a freq update) when a CPU
   enters IDLE; this might not work well, though, as we probably want
   to keep in blocked util contribution for a bit

What you think is the way to go?

Thanks,

- Juri