linux-kernel - Re: [RFC PATCH v3 2/3] docs: scheduler: Add scheduler overview documentation

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Date:   Fri, 8 May 2020 12:58:36 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Valentin Schneider <valentin.schneider@....com>,
        John Mathew <john.mathew@...kie.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        corbet@....net, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, tsbogend@...ha.franken.de,
        lukas.bulwahn@...il.com, x86@...nel.org,
        linux-mips@...r.kernel.org, tglx@...utronix.de,
        mostafa.chamanara@...emark.com, rdunlap@...radead.org,
        Oleg Tsymbal <oleg.tsymbal@...kie.com>
Subject: Re: [RFC PATCH v3 2/3] docs: scheduler: Add scheduler overview
 documentation

On 07/05/2020 23:15, Valentin Schneider wrote:
> 
> On 07/05/20 19:05, John Mathew wrote:

[...]

> It would also be an opportunity to have one place to (at least briefly)
> describe what the different sched classes do wrt capacity asymmetry - CFS
> does one thing, RT now does one thing (see Qais' work), and DL will
> hopefully soon follow (see Dietmar's work).
> 
> I'd be happy to contribute (some of) that, if it can be deemed useful (I
> personally think it might).

I like the idea.

Essentially all the code which is guarded by the 'if
(static_branch_unlikely(&sched_asym_cpucapacity)' condition or which
sets it during bring-up.

* 'Cpu capacity < SCHED_LOAD_SCALE for non-big' CPUs setting during
   bringup (necessary dt binding, CPUfreq influence)

* CFS capacity awareness:

  * wakeup - select_idle_capacity() (replaced wake_cap() & slow path to
             cover DynamIQ and classical big.LITTLE)

  * load_balance - misfit handling

* RT & DL capacity awareness

* ... & the relation to EAS (Documentation/scheduler/sched-energy.rst)

This is what we referred to (at least internally) as CAS (Capacity-Aware
Scheduling).