linux-kernel - Re: [PATCH 2/4] sched/fair: cleanup loop_max and loop

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Date:   Mon, 12 Sep 2022 10:45:00 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org
Cc:     zhangqiao22@...wei.com
Subject: Re: [PATCH 2/4] sched/fair: cleanup loop_max and loop_break

On 25/08/2022 14:27, Vincent Guittot wrote:
> sched_nr_migrate_break is set to a fix value and never changes so we can
> replace it by a define SCHED_NR_MIGRATE_BREAK.
> 
> Also, we adjust SCHED_NR_MIGRATE_BREAK to be aligned with the init value
> of sysctl_sched_nr_migrate which can be init to different values.
> 
> Then, use SCHED_NR_MIGRATE_BREAK to init sysctl_sched_nr_migrate.
> 
> The behavior stays unchanged unless you modify sysctl_sched_nr_migrate
> trough debugfs.

I don't quite get this sentence. The behavior would potentially change
if you change sysctl_sched_nr_migrate before this patch too?

> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/sched/core.c  |  6 +-----
>  kernel/sched/fair.c  | 11 ++++-------
>  kernel/sched/sched.h |  6 ++++++
>  3 files changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 64c08993221b..a21e817bdd1c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -142,11 +142,7 @@ __read_mostly int sysctl_resched_latency_warn_once = 1;
>   * Number of tasks to iterate in a single balance run.
>   * Limited because this is done with IRQs disabled.
>   */

    ^^^
Shouldn't this comment be removed as well?

> -#ifdef CONFIG_PREEMPT_RT
> -const_debug unsigned int sysctl_sched_nr_migrate = 8;
> -#else
> -const_debug unsigned int sysctl_sched_nr_migrate = 32;
> -#endif
> +const_debug unsigned int sysctl_sched_nr_migrate = SCHED_NR_MIGRATE_BREAK;
>  
>  __read_mostly int scheduler_running;

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