Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

From	Patrick Bellasi <patrick.bellasi@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable
Date	2016-03-17 17:00 +0100
Message-ID	<rdIv7-Qo-1@gated-at.bofh.it> (permalink)
References	(5 earlier) <rdeGL-6bc-17@gated-at.bofh.it> <rdgyS-7xF-11@gated-at.bofh.it> <rdnTI-3JO-27@gated-at.bofh.it> <rdCzo-5z7-17@gated-at.bofh.it> <rdGD0-87J-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 17-Mar 06:55, Steve Muckle wrote:
> On 03/17/2016 02:40 AM, Juri Lelli wrote:
> >> Could the default schedtune value not serve as the out of the box margin?
> >>
> > I'm not sure I understand you here. For me schedtune should be disabled
> > by default, so I'd say that it doesn't introduce any additional margin
> > by default. But we still need a margin to make the governor work without
> > schedtune in the mix.
> 
> Why not have schedtune be enabled always, and use it to add the margin?
> It seems like it'd simplify things.

Actually one of the effects we noticed when SchedTune and SchedFreq
are both in use is that we have a sort of "double boosting" effect.

SchedTune boosts the CPU utilization signal, thus already providing a
sort of margin for the selection of the OPP. This margin overlaps with
the SchedFreq margin, which in turns could results in the selection of
an OPP even more higher than required (with boost already accouned).

> I haven't looked at the schedtune code at all so I don't know whether
> this makes sense given its current implementation.

The current implementation requires review, of course ;-)
Last (and only) posting is based on top of SchedFreq code, as it was
at that time.

> But conceptually I don't know why we'd need or want one margin in
> schedutil which will be tunable, and then another mechanism for
> tuning as well.

I agree with Steve on the conceptual standpoint. The main goal of
SchedTune is actually to provide a "single tunable" to bias many
different subsystem in a "consistent" way. Thus, from a conceptual
standpoint, IMO it makes sens to investigate better how the boost value
can be linked with SchedFreq.

A possible option can be to:
1. use an hardcoded margin (M) defined by SchedFreq
   this margin is used to trigger OPP jumps
   when SchedTune _is not_ in use
2. "compose" the M margin with a boost value defined margin (B)
   when SchedTune _is_ in use

This means, e.g.
  schedfreq_margin = max(M, B)
Thus:
a) non boosted tasks (and in general when SchedTune is not in use)
   gets OPPs jumps based on the hardcoded M margin
b) boosted tasks can get more aggressive OPPs jumps based on the B
   margin

While the M margin is hardcoded, the B one is defined via CGroups
depending on the how much tasks needs to be boosted.

-- 
#include <best/regards.h>

Patrick Bellasi

Thread

[PATCH 0/8] schedutil enhancements Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
  [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:30 +0100
      Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:50 +0100
        Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 04:40 +0100
          Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Peter Zijlstra <peterz@infradead.org> - 2016-03-16 09:10 +0100
            Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Juri Lelli <Juri.Lelli@arm.com> - 2016-03-16 11:10 +0100
              Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 19:00 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-16 23:10 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Juri Lelli <Juri.Lelli@arm.com> - 2016-03-17 10:40 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Steve Muckle <steve.muckle@linaro.org> - 2016-03-17 15:00 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Patrick Bellasi <patrick.bellasi@arm.com> - 2016-03-17 17:00 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Juri Lelli <Juri.Lelli@arm.com> - 2016-03-17 19:00 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-17 20:00 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-17 23:40 +0100
            Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-16 13:50 +0100
          Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-16 23:10 +0100
  [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:20 +0100
      Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Peter Zijlstra <peterz@infradead.org> - 2016-03-15 23:00 +0100
    Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Peter Zijlstra <peterz@infradead.org> - 2016-03-16 09:10 +0100
  [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:30 +0100
      Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 05:00 +0100
      Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 08:50 +0100
        Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-16 09:40 +0100
          Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 10:00 +0100
            Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-16 10:20 +0100
            Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-16 13:40 +0100
              Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 14:20 +0100
                Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-16 14:30 +0100
                Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 14:50 +0100
  [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-03-15 20:20 +0100
      Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Michael Turquette <mturquette@baylibre.com> - 2016-03-15 21:50 +0100
        Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-03-16 20:50 +0100
          Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-16 21:10 +0100
            Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-16 22:40 +0100
    Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:50 +0100
      Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-16 08:50 +0100
        Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-16 13:50 +0100
  [PATCH 2/8] sched/fair: add margin to utilization update Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    Re: [PATCH 2/8] sched/fair: add margin to utilization update Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:20 +0100
      Re: [PATCH 2/8] sched/fair: add margin to utilization update Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:50 +0100
    Re: [PATCH 2/8] sched/fair: add margin to utilization update Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 04:00 +0100
      Re: [PATCH 2/8] sched/fair: add margin to utilization update Michael Turquette <mturquette@baylibre.com> - 2016-03-16 23:20 +0100
  [PATCH 3/8] sched/cpufreq: new cfs capacity margin helpers Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    Re: [PATCH 3/8] sched/cpufreq: new cfs capacity margin helpers Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:20 +0100
  Re: [PATCH 0/8] schedutil enhancements "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-16 01:10 +0100

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