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Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow

From Steve Muckle <steve.muckle@linaro.org>
Newsgroups linux.kernel
Subject Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow
Date 2016-02-26 02:20 +0100
Message-ID <r6fez-40K-29@gated-at.bofh.it> (permalink)
References <r59Xz-6rQ-1@gated-at.bofh.it> <r59XA-6rQ-21@gated-at.bofh.it> <r5a7i-6wg-29@gated-at.bofh.it> <r6f4T-3Xh-47@gated-at.bofh.it>
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On 02/25/2016 04:50 PM, Michael Turquette wrote:
>> > Something more sophisticated than this is needed, because one driver
>> > may actually be able to do "fast" switching in some cases and may not
>> > be able to do that in other cases.
>
> Those drivers can set the flag dynamically when they probe based on
> their ACPI tables.

I was thinking that the reference here was to a driver that may be able
to do fast switching for some transitions and not for others, say
perhaps depending on the current and target frequencies, or the state of
the regulators, or other system conditions.

Rafael has proposed a fast_switch() addition to the cpufreq API which
currently returns void. Perhaps that could be extended to return success
or failure from the driver. The driver aborts if it cannot complete the
request atomically and quickly.

The scheduler-driven governor could attempt a fast switch if the
callback is installed (and the other criteria for the fast switch are
met, such as not throttled etc, no request already in flight etc). If
the fast switch aborts, fall back to the slow path.

I suppose the governor could also just see if policy->cur has changed as
opposed to checking cpufreq_driver_fast_switch's return value. But then
we can't tell the difference between the fast transition failing because
it must be re-attempted in the slow path, and the fast transition
failing because of some other more serious reason. In the latter case
the request should probably just be dropped rather than retried in the
slow path.

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[RFCv7 PATCH 00/10] sched: scheduler-driven CPU frequency selection Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 07/10] sched/fair: jump to max OPP when crossing UP threshold Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 09/10] sched/deadline: split rt_avg in 2 distincts metrics Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 10/10] sched: rt scheduler sets capacity requirement Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 08/10] sched: remove call of sched_avg_update from sched_rt_avg_update Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
    Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-23 02:40 +0100
      Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow Michael Turquette <mturquette@baylibre.com> - 2016-02-26 02:10 +0100
        Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-26 02:20 +0100
          Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-26 22:10 +0100
        Re: [RFCv7 PATCH 02/10] cpufreq: introduce cpufreq_driver_is_slow Steve Muckle <steve.muckle@linaro.org> - 2016-02-26 02:20 +0100
  [RFCv7 PATCH 06/10] sched/fair: cpufreq_sched triggers for load balancing Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 04/10] sched/fair: add triggers for OPP change requests Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
    Re: [RFCv7 PATCH 04/10] sched/fair: add triggers for OPP change requests Ricky Liang <jcliang@chromium.org> - 2016-03-01 08:00 +0100
      Re: [RFCv7 PATCH 04/10] sched/fair: add triggers for OPP change  requests Steve Muckle <steve.muckle@linaro.org> - 2016-03-03 05:00 +0100
  [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
    Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-25 05:00 +0100
      Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-02-25 10:30 +0100
        Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-25 22:10 +0100
      Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-02-25 10:30 +0100
        Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-25 22:10 +0100
          Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-02-26 10:20 +0100
            Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-27 01:10 +0100
              Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-03-01 14:00 +0100
                Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-01 20:50 +0100
      Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-25 12:10 +0100
      Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Steve Muckle <steve.muckle@linaro.org> - 2016-02-26 01:40 +0100
        Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-27 03:40 +0100
          Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Steve Muckle <steve.muckle@linaro.org> - 2016-02-27 05:20 +0100
            Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-28 03:30 +0100
              Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-03-01 15:40 +0100
                Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-01 21:40 +0100
            Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-03-01 14:30 +0100
        Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-03-01 14:20 +0100
        Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection Michael Turquette <mturquette@baylibre.com> - 2016-03-02 08:50 +0100
          Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-03 03:50 +0100
            Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Steve Muckle <steve.muckle@linaro.org> - 2016-03-03 05:00 +0100
              Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Juri Lelli <Juri.Lelli@arm.com> - 2016-03-03 10:40 +0100
          Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Peter Zijlstra <peterz@infradead.org> - 2016-03-03 14:10 +0100
    Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency  selection Ingo Molnar <mingo@kernel.org> - 2016-03-03 15:30 +0100
  [RFCv7 PATCH 05/10] sched/{core,fair}: trigger OPP change request on fork() Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
  [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at current frequency Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:30 +0100
    Re: [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at  current frequency "Rafael J. Wysocki" <rafael@kernel.org> - 2016-02-23 02:50 +0100
      Re: [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at  current frequency Peter Zijlstra <peterz@infradead.org> - 2016-02-23 10:20 +0100
        Re: [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at current frequency "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-02-26 02:40 +0100
          Re: [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at  current frequency Peter Zijlstra <peterz@infradead.org> - 2016-02-26 10:20 +0100
  Re: [RFCv7 PATCH 00/10] sched: scheduler-driven CPU frequency  selection Steve Muckle <steve.muckle@linaro.org> - 2016-02-23 02:40 +0100

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