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Date: Mon, 21 Nov 2016 15:43:43 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Juri Lelli <Juri.Lelli@arm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
        Rafael Wysocki <rjw@rjwysocki.net>, Ingo Molnar <mingo@redhat.com>,
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        Steve Muckle <smuckle.linux@gmail.com>, tkjos@google.com,
        Morten Rasmussen <morten.rasmussen@arm.com>
Subject: Re: [PATCH] cpufreq: schedutil: add up/down frequency transition
 rate limits
Message-ID: <20161121144343.GH3092@twins.programming.kicks-ass.net>
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On Mon, Nov 21, 2016 at 02:37:27PM +0000, Juri Lelli wrote:
> On 21/11/16 15:17, Peter Zijlstra wrote:

> > Not sure I follow. So by limiting decay to the task value, the moment we
> > add it back to the accumulated signal (wakeup), the accumulated signal
> > jumps up quickly and ramp-up is achieved.
> > 
> 
> This is true, but it seems that this potentially spiky behaviour
> (which in general depends on tasks composition and periodicity) might
> affect power savings (as in you don't generally want to switch between
> high and low freqs too often). So that's why I was just thinking that
> some sort of smoothing applied to the signal schedutil uses might help.

Hurm.. so during LPC it was said that fast ramp-up was desired. Note
that we'll not ramp down this fast, the accumulated signal will decay
slowly as per blocked-load PELT rules. So only ramp-up is spiky, but
that is what was desired AFAIU.