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Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to SCHED_FIFO task

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On Sun, Nov 13, 2016 at 03:37:18PM +0100, Rafael J. Wysocki wrote:
> > Hold on a sec. I thought during LPC someone (Peter?) made a point that when
> > RT thread run, we should bump the frequency to max? So, schedutil is going
> > to trigger schedutil to bump up the frequency to max, right?
> 
> No, it isn't, or at least that is unlikely.
> 
> sugov_update_commit() sets sg_policy->work_in_progress before queuing
> the IRQ work and it is not cleared until the frequency changes in
> sugov_work().
> 
> OTOH, sugov_should_update_freq() checks sg_policy->work_in_progress
> upfront and returns false when it is set, so the governor won't see
> its own worker threads run, unless I'm overlooking something highly
> non-obvious.

FWIW my intention with the original version of this patch (which I
neglected to communicate to Viresh) was that it would depend on changing
the frequency policy for RT. I had been using rt_avg. It sounds like
during LPC there were talks of using another metric.

It does appear things would work okay without that but it also seems
a bit fragile. There's the window between when the work_in_progress
gets cleared and the RT kthread yields. I have not thought through the
various scenarios there, what is possible and tested to see if it is
significant enough to impact power-sensitive platforms.

thanks,
Steve

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Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task "Rafael J. Wysocki" <rafael@kernel.org> - 2016-11-11 23:20 +0100
  Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue  to SCHED_FIFO task Saravana Kannan <skannan@codeaurora.org> - 2016-11-12 02:40 +0100
    Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-12 06:30 +0100
      Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-14 06:40 +0100
    Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task "Rafael J. Wysocki" <rafael@kernel.org> - 2016-11-13 15:40 +0100
      Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task Steve Muckle <smuckle.linux@gmail.com> - 2016-11-13 20:50 +0100
        Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task "Rafael J. Wysocki" <rafael@kernel.org> - 2016-11-13 23:50 +0100
          Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-14 07:40 +0100
  Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task Viresh Kumar <viresh.kumar@linaro.org> - 2016-11-12 06:30 +0100
  Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to  SCHED_FIFO task Steve Muckle <smuckle.linux@gmail.com> - 2016-11-13 21:00 +0100

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