linux-kernel - Re: [PATCH v3 6/7] sched/topology: Introduce SD metaflag for flags needing

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Date:   Thu, 2 Jul 2020 20:29:27 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Valentin Schneider <valentin.schneider@....com>,
        linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        vincent.guittot@...aro.org, morten.rasmussen@....com
Subject: Re: [PATCH v3 6/7] sched/topology: Introduce SD metaflag for flags
 needing > 1 groups

On 01/07/2020 21:06, Valentin Schneider wrote:

[...]

> @@ -105,16 +122,18 @@ SD_FLAG(SD_SERIALIZE,           8, SDF_SHARED_PARENT)
>   * Place busy tasks earlier in the domain
>   *
>   * SHARED_CHILD: Usually set on the SMT level. Technically could be set further
> - * up, but currently assumed to be set from the base domain upwards (see
> - * update_top_cache_domain()).
> + *               up, but currently assumed to be set from the base domain
> + *               upwards (see update_top_cache_domain()).
>   */
> -SD_FLAG(SD_ASYM_PACKING,        9, SDF_SHARED_CHILD)
> +SD_FLAG(SD_ASYM_PACKING,        9, SDF_SHARED_CHILD | SDF_NEEDS_GROUPS)
>  
>  /*
>   * Prefer to place tasks in a sibling domain
>   *
>   * Set up until domains start spanning NUMA nodes. Close to being a SHARED_CHILD
>   * flag, but cleared below domains with SD_ASYM_CPUCAPACITY.
> + *
> + * NEEDS_GROUPS: Load balancing flag.
>   */
>  SD_FLAG(SD_PREFER_SIBLING,      10, 0)

Related to my comment in [PATCH v3 5/7], maybe you wanted to add
SDF_NEEDS_GROUPS for SD_PREFER_SIBLING as well ? This comment
'NEEDS_GROUPS: Load balancing flag.' makes me wondering.

Currently, SD_PREFER_SIBLING isn't in SD_DEGENERATE_GROUPS_MASK=0xaef.

[...]