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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Fri, 15 Apr 2022 10:32:09 +0200
Message-ID: <CAKfTPtAbxAerbV-LBcpm_qHAphhD3uU47k0hu=DDX3k6LS-Aow@mail.gmail.com>
Subject: Re: [PATCH V1 RESEND]: sched/fair: Revise comment about lb decision matrix
To:     Tao Zhou <tao.zhou@linux.dev>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>
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On Fri, 15 Apr 2022 at 04:22, Tao Zhou <tao.zhou@linux.dev> 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().

The behavior has changed with
cad68e552e77 ("sched/fair: Consider misfit tasks when load-balancing")
But we haven't updated the matrix

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


> 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
>
> Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()")
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Signed-off-by: Tao Zhou <tao.zhou@linux.dev>
> ---
>
> v1 changelog:
> (1) Send to MAINTAINERS/REVIEWS get from `./scripts/get_maintainer.pl`
>     suggested by Dietmar Eggemann.
> (2) Based on v5.18-rc2
>
>
>  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 d4bd299d67ab..b8c67e7c8cf3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9495,7 +9495,7 @@ 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
> --
> 2.35.2
>