linux-kernel - Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits

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Message-ID: <CANRm+CzQ3H1YJEcAJk4pwFJ+v4c0nFSNu5G+kx_e7Y1XWz1rNQ@mail.gmail.com>
Date:   Thu, 29 Dec 2016 11:24:56 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Juri Lelli <Juri.Lelli@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Robin Randhawa <robin.randhawa@....com>,
        Steve Muckle <smuckle.linux@...il.com>, tkjos@...gle.com,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits

2016-11-21 20:26 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> On Mon, Nov 21, 2016 at 12:14:32PM +0000, Juri Lelli wrote:
>> On 21/11/16 11:19, Peter Zijlstra wrote:
>
>> > So no tunables and rate limits here at all please.
>> >
>> > During LPC we discussed the rampup and decay issues and decided that we
>> > should very much first address them by playing with the PELT stuff.
>> > Morton was going to play with capping the decay on the util signal. This
>> > should greatly improve the ramp-up scenario and cure some other wobbles.
>> >
>> > The decay can be set by changing the over-all pelt decay, if so desired.
>> >
>>
>> Do you mean we might want to change the decay (make it different from
>> ramp-up) once for all, or maybe we make it tunable so that we can
>> address different power/perf requirements?
>
> So the limited decay would be the dominant factor in ramp-up time,
> leaving the regular PELT period the dominant factor for ramp-down.
>
> (Note that the decay limit would only be applied on the per-task signal,
> not the accumulated signal.)

What's the meaning of "signal" in this thread?

Regards,
Wanpeng Li