linux-kernel - Re: [PATCH] sched/fair: Revise comment about lb decision matrix

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Message-ID: <a443f8ed-7bc9-5ded-89de-b19fad014359@arm.com>
Date:   Thu, 14 Apr 2022 12:33:06 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Tao Zhou <tao.zhou@...ux.dev>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Revise comment about lb decision matrix

On 03/04/2022 19:59, Tao Zhou wrote:
> If busiest group type is group_misfit_task, the local
> group type must be group_has_spare according to below
> code in update_sd_pick_busiest():
> 
> if (sgs->group_type == group_misfit_task &&
>     (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) ||
>      sds->local_stat.group_type != group_has_spare))
>          return false;
> 
> group type imbalanced and overloaded and fully_busy are filtered in here.
> misfit and asym are filtered before in update_sg_lb_stats().
> So, change the decision matrix to:
> 
> busiest \ local has_spare fully_busy misfit asym imbalanced overloaded
> has_spare        nr_idle   balanced   N/A    N/A  balanced   balanced
> fully_busy       nr_idle   nr_idle    N/A    N/A  balanced   balanced
> misfit_task      force     N/A        N/A    N/A  *N/A*      *N/A*
> asym_packing     force     force      N/A    N/A  force      force
> imbalanced       force     force      N/A    N/A  force      force
> overloaded       force     force      N/A    N/A  force      avg_load
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5146163bfabb..5765d96202c7 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9441,7 +9441,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>   * busiest \ local has_spare fully_busy misfit asym imbalanced overloaded
>   * has_spare        nr_idle   balanced   N/A    N/A  balanced   balanced
>   * fully_busy       nr_idle   nr_idle    N/A    N/A  balanced   balanced
> - * misfit_task      force     N/A        N/A    N/A  force      force
> + * misfit_task      force     N/A        N/A    N/A  N/A        N/A
>   * asym_packing     force     force      N/A    N/A  force      force
>   * imbalanced       force     force      N/A    N/A  force      force
>   * overloaded       force     force      N/A    N/A  force      avg_load

You should put people you find in `./scripts/get_maintainer.pl
kernel/sched/fair.c` on To/Cc to attract more attention.

Otherwise, LGTM.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>