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

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Message-ID: <jhjd07etqvo.mognet@arm.com>
Date:   Fri, 08 May 2020 15:58:51 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     John Mathew <john.mathew@...kie.com>, 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 08/05/20 11:58, Dietmar Eggemann wrote:
> 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).

Yeah, something like that. I'll sharpen my quill and have a go at it,
though it won't be for right now with OSPM and the other ongoing stuff.