Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 10 Nov 2016 01:13:49 +0100 | Subject | Re: [Resend][PATCH] cpufreq: conservative: Decrease frequency faster when the timer deferred |
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On Wed, Nov 9, 2016 at 6:55 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: > On 08-11-16, 21:25, Stratos Karafotis wrote: >> But this is the supposed behaviour of conservative governor. We want >> the CPU to increase the frequency in steps. The patch just resets >> the frequency to a lower frequency in case of idle. >> >> For argument's sake, let's assume that the governor timer is never >> deferred and runs every sampling period even on completely idle CPU. > > There are no timers now :) > >> And let's assume, for example, a burst load that runs every 100ms >> for 20ms. The default sampling rate is also 20ms. >> What would conservative do in case of that burst load? It would >> increase the frequency by one freq step after 20ms and then it would >> decrease the frequency 4 times by one frequency step. Most probably >> on the next burst load, the CPU will run on min frequency. >> >> I agree that maybe this is not ideal for performance but maybe this is >> how we want conservative governor to work (lazily increase and decrease >> frequency). > > Idle periods are already accounted for while calculating system load by legacy > governors. > > And the more and more I think about this, I am inclined towards your patch. > Maybe in a bit different form and commit log. > > If we see how the governors were written initially, there were no deferred > timers. And so even if CPUs were idle, we will wake up to adjust the step. > > Even if we want to make the behavior similar to that, then also we should > account of missed sampling periods both while decreasing or increasing > frequencies. > > @Rafael: What do you think ?
It looks like the issue with the conservative governor is real, but I'm a bit concerned about adding things to use by one particular governor only to cpufreq_governor.c.
Apart from the timer-related terminology that is not applicable any more, of course.
Thanks, Rafael
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