linux-kernel - Re: [PATCH v2 2/3] sched/fair: Do strict inequality check for busiest misfit task group

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Date: Sun, 4 Feb 2024 12:45:18 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: David Vernet <void@...ifault.com>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, peterz@...radead.org, 
	juri.lelli@...hat.com, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, 
	kernel-team@...a.com
Subject: Re: [PATCH v2 2/3] sched/fair: Do strict inequality check for busiest
 misfit task group

On Sun, 4 Feb 2024 at 05:46, David Vernet <void@...ifault.com> wrote:
>
> In update_sd_pick_busiest(), when comparing two sched groups that are
> both of type group_misfit_task, we currently consider the new group as
> busier than the current busiest group even if the new group has the
> same misfit task load as the current busiest group. We can avoid some
> unnecessary writes if we instead only consider the newest group to be
> the busiest if it has a higher load than the current busiest. This
> matches the behavior of other group types where we compare load, such as
> two groups that are both overloaded.
>
> Let's update the group_misfit_task type comparison to also only update
> the busiest group in the event of strict inequality.

fair enough

Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

>
> Signed-off-by: David Vernet <void@...ifault.com>
> ---
>  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 e7519ea434b1..76d03106040d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10028,7 +10028,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
>                  * If we have more than one misfit sg go with the biggest
>                  * misfit.
>                  */
> -               if (sgs->group_misfit_task_load < busiest->group_misfit_task_load)
> +               if (sgs->group_misfit_task_load <= busiest->group_misfit_task_load)
>                         return false;
>                 break;
>
> --
> 2.43.0
>