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Subject: Re: [RFC PATCH v3 2/3] docs: scheduler: Add scheduler overview
 documentation
To:     Valentin Schneider <valentin.schneider@arm.com>,
        John Mathew <john.mathew@unikie.com>
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        lukas.bulwahn@gmail.com, x86@kernel.org,
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        Oleg Tsymbal <oleg.tsymbal@unikie.com>
References: <20200507180553.9993-1-john.mathew@unikie.com>
 <20200507180553.9993-3-john.mathew@unikie.com> <jhjh7wrtpjk.mognet@arm.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <b974b959-7b9a-2874-dca6-674b74ad5b42@arm.com>
Date:   Fri, 8 May 2020 12:58:36 +0200
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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).