linux-kernel - Re: [PATCH v4 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched

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Date:   Tue, 18 May 2021 15:39:27 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Beata Michalska <beata.michalska@....com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        "corbet@....net" <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL
 sched_domain flag

On Mon, 17 May 2021 at 10:24, Beata Michalska <beata.michalska@....com> wrote:
>
> Introducing new, complementary to SD_ASYM_CPUCAPACITY, sched_domain
> topology flag, to distinguish between shed_domains where any CPU
> capacity asymmetry is detected (SD_ASYM_CPUCAPACITY) and ones where
> a full range of CPU capacities is visible to all domain members
> (SD_ASYM_CPUCAPACITY_FULL).

I'm not sure about what you want to detect:

Is it a sched_domain level with a full range of cpu capacity, i.e.
with at least 1 min capacity and 1 max capacity ?
or do you want to get at least 1 cpu of each capacity ?


>
> With the distinction between full and partial CPU capacity asymmetry,
> brought in by the newly introduced flag, the scope of the original
> SD_ASYM_CPUCAPACITY flag gets shifted, still maintaining the existing
> behaviour when one is detected on a given sched domain, allowing
> misfit migrations within sched domains that do not observe full range
> of CPU capacities but still do have members with different capacity
> values. It loses though it's meaning when it comes to the lowest CPU
> asymmetry sched_domain level per-cpu pointer, which is to be now
> denoted by SD_ASYM_CPUCAPACITY_FULL flag.
>
> Signed-off-by: Beata Michalska <beata.michalska@....com>
> Reviewed-by: Valentin Schneider <valentin.schneider@....com>
> ---
>  include/linux/sched/sd_flags.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h
> index 34b21e9..57bde66 100644
> --- a/include/linux/sched/sd_flags.h
> +++ b/include/linux/sched/sd_flags.h
> @@ -91,6 +91,16 @@ SD_FLAG(SD_WAKE_AFFINE, SDF_SHARED_CHILD)
>  SD_FLAG(SD_ASYM_CPUCAPACITY, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS)
>
>  /*
> + * Domain members have different CPU capacities spanning all unique CPU
> + * capacity values.
> + *
> + * SHARED_PARENT: Set from the topmost domain down to the first domain where
> + *               all available CPU capacities are visible
> + * NEEDS_GROUPS: Per-CPU capacity is asymmetric between groups.
> + */
> +SD_FLAG(SD_ASYM_CPUCAPACITY_FULL, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS)
> +
> +/*
>   * Domain members share CPU capacity (i.e. SMT)
>   *
>   * SHARED_CHILD: Set from the base domain up until spanned CPUs no longer share
> --
> 2.7.4
>