linux-kernel - Re: [PATCH 1/1] sched/fair:Reduce unnecessary check preempt in the sched tick

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Message-ID: <YHWpknBamqQz2rpJ@hirez.programming.kicks-ass.net>
Date:   Tue, 13 Apr 2021 16:24:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     qianjun.kernel@...il.com
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] sched/fair:Reduce unnecessary check preempt in the
 sched tick

On Tue, Apr 13, 2021 at 09:18:42PM +0800, qianjun.kernel@...il.com wrote:
> From: jun qian <qianjun.kernel@...il.com>
> 
> If it has been determined that the current cpu need resched in the
> early stage of for_each_sched_entity, then there is no need to check
> preempt in the subsequent se->parent entity_tick.

Right, but does it actually do anything, except increase linecount?

> Signed-off-by: jun qian <qianjun.kernel@...il.com>
> ---
>  kernel/sched/fair.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a0536add..c0d135100d54 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4352,8 +4352,13 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
>  {
>  	unsigned long ideal_runtime, delta_exec;
>  	struct sched_entity *se;
> +	struct rq *rq = rq_of(cfs_rq);
>  	s64 delta;
>  
> +	/* If the TIF_NEED_RESCHED has been set, it is no need to check again */
> +	if (test_tsk_need_resched(rq->curr))
> +		return;
> +
>  	ideal_runtime = sched_slice(cfs_rq, curr);
>  	delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
>  	if (delta_exec > ideal_runtime) {

Also, I think that's placed wrong; this way we can mis clear_buddies().