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

From	Juri Lelli <Juri.Lelli@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable
Date	2016-03-17 19:00 +0100
Message-ID	<rdKnh-22V-19@gated-at.bofh.it> (permalink)
References	(5 earlier) <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> <rdIv7-Qo-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Hi,

On 17/03/16 15:53, Patrick Bellasi wrote:
> 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.
> 

Makes sense to me. And I think M margin is the one we don't want to make
part of the ABI and only play with it under DEBUG.

Best,

- Juri

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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