linux-kernel - Re: Re: [PATCH 1/2] sched/fair: Do not let idle entities preempt others

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Message-ID: <e7a81f13-6f09-4a7a-9d85-0ba4885442bc@bytedance.com>
Date: Sun, 23 Feb 2025 16:45:54 +0800
From: Abel Wu <wuyun.abel@...edance.com>
To: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Cc: "open list:SCHEDULER" <linux-kernel@...r.kernel.org>,
 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>, Josh Don <joshdon@...gle.com>,
 Valentin Schneider <vschneid@...hat.com>,
 Tianchen Ding <dtcccc@...ux.alibaba.com>
Subject: Re: Re: [PATCH 1/2] sched/fair: Do not let idle entities preempt
 others

On 2/23/25 1:48 AM, Madadi Vineeth Reddy Wrote:
> On 21/02/25 16:42, Abel Wu wrote:
>> A task with SCHED_IDLE policy doesn't preempt others by definition, and
>> the semantics are intended to be preserved when extending to cgroups
>> introduced in commit 304000390f88 ("sched: Cgroup SCHED_IDLE support").
> 
> [snip]
> 
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 1c0ef435a7aa..4340178f29b7 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -8778,12 +8778,15 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
>>   	pse_is_idle = se_is_idle(pse);
>>   
>>   	/*
>> -	 * Preempt an idle entity in favor of a non-idle entity (and don't preempt
>> -	 * in the inverse case).
>> +	 * Preempt an idle entity in favor of a non-idle entity.
>>   	 */
>>   	if (cse_is_idle && !pse_is_idle)
>>   		goto preempt;
> 
> This patch doesn't apply cleanly on top of tip/sched/core because of the
> commit f553741ac8c0 ("sched: Cancel the slice protection of the idle entity").
> Please rebase it.

Will rebase. Thanks!

> 
> Thanks,
> Madadi Vineeth Reddy
> 
>> -	if (cse_is_idle != pse_is_idle)
>> +
>> +	/*
>> +	 * IDLE entities do not preempt others.
>> +	 */
>> +	if (unlikely(pse_is_idle))
>>   		return;
>>   
>>   	/*
>