linux-kernel - Re: [PATCH v2] sched/fair: merge same code in enqueue_task

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Date:   Wed, 13 Dec 2023 16:18:55 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     WangJinchao <wangjinchao@...sion.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     stone.xulei@...sion.com
Subject: Re: [PATCH v2] sched/fair: merge same code in enqueue_task_fair

Hi Jinchao,

On 12/13/23 3:12 PM, WangJinchao Wrote:
> The code below is duplicated in two for loops and need to be
>     consolidated

It doesn't need to, but it can actually bring some benefit from
the point of view of text size, especially in warehouse-scale
computers where icache is extremely contended.

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-56 (-56)
Function                                     old     new   delta
enqueue_task_fair                            936     880     -56
Total: Before=64899, After=64843, chg -0.09%

> 
> Signed-off-by: WangJinchao <wangjinchao@...sion.com>
> ---
>   kernel/sched/fair.c | 31 ++++++++-----------------------
>   1 file changed, 8 insertions(+), 23 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d7a3c63a2171..e1373bfd4f2e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6681,30 +6681,15 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>   		cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
>   
>   	for_each_sched_entity(se) {
> -		if (se->on_rq)
> -			break;
>   		cfs_rq = cfs_rq_of(se);
> -		enqueue_entity(cfs_rq, se, flags);
> -
> -		cfs_rq->h_nr_running++;
> -		cfs_rq->idle_h_nr_running += idle_h_nr_running;
> -
> -		if (cfs_rq_is_idle(cfs_rq))
> -			idle_h_nr_running = 1;
> -
> -		/* end evaluation on encountering a throttled cfs_rq */
> -		if (cfs_rq_throttled(cfs_rq))
> -			goto enqueue_throttle;
> -
> -		flags = ENQUEUE_WAKEUP;
> -	}
> -
> -	for_each_sched_entity(se) {
> -		cfs_rq = cfs_rq_of(se);
> -
> -		update_load_avg(cfs_rq, se, UPDATE_TG);
> -		se_update_runnable(se);
> -		update_cfs_group(se);
> +		if (se->on_rq) {
> +			update_load_avg(cfs_rq, se, UPDATE_TG);
> +			se_update_runnable(se);
> +			update_cfs_group(se);
> +		} else {
> +			enqueue_entity(cfs_rq, se, flags);
> +			flags = ENQUEUE_WAKEUP;
> +		}
>   
>   		cfs_rq->h_nr_running++;
>   		cfs_rq->idle_h_nr_running += idle_h_nr_running;

I have no strong opinon about this 'cleanup', but the same pattern
can also be found in dequeue_task_fair() and I think it would be
better get them synchronized.

Thanks,
	Abel