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

From	Viresh Kumar <viresh.kumar@linaro.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits
Date	2016-11-21 12:40 +0100
Message-ID	<sFV73-yJ-7@gated-at.bofh.it> (permalink)
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On 21-11-16, 12:12, Peter Zijlstra wrote:
> I think it should be replaced by a value provided by the driver. It
> makes sense to have a rate-limit in so far as that it doesn't make sense
> to try and program the hardware faster than it can actually change
> frequencies and/or have a programming cost amortization. And this very
> clearly is a driver specific thing.

We already have something called as transition_latency for that (though it isn't
used much currently).

> It however doesn't make sense to me to fudge with this in order to
> achieve ramp up/down differences.

So if a platform, for example, can do DVFS in say 100-500 us, then the scheduler
should try to re-evaluate frequency (and update it) after that short of a
period? Wouldn't that scheme waste lots of time doing just freq updates? And
that's the primary reason why cpufreq governors have some sort of sampling-rate
or rate-limit until now.

-- 
viresh

Thread

[PATCH] cpufreq: schedutil: add up/down frequency transition rate limits Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-17 06:30 +0100
  Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-21 11:10 +0100
    Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 11:20 +0100
      Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-21 11:50 +0100
        Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 12:20 +0100
          Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-21 12:40 +0100
            Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 12:50 +0100
      Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Juri Lelli <Juri.Lelli@arm.com> - 2016-11-21 13:20 +0100
        Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 13:30 +0100
          Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Juri Lelli <Juri.Lelli@arm.com> - 2016-11-21 15:00 +0100
            Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 15:20 +0100
              Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Juri Lelli <Juri.Lelli@arm.com> - 2016-11-21 15:40 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 15:50 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Juri Lelli <Juri.Lelli@arm.com> - 2016-11-21 16:00 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-22 10:30 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Patrick Bellasi <patrick.bellasi@arm.com> - 2016-11-22 12:10 +0100
            Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Patrick Bellasi <patrick.bellasi@arm.com> - 2016-11-21 16:00 +0100
              Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 16:30 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 16:40 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Patrick Bellasi <patrick.bellasi@arm.com> - 2016-11-21 17:30 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition  rate limits Peter Zijlstra <peterz@infradead.org> - 2016-11-21 17:50 +0100
                Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits "Rafael J. Wysocki" <rafael@kernel.org> - 2016-11-21 22:00 +0100

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