linux-kernel - Re: [PATCH] sched/fair: Optimize dequeue_task

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Date:   Tue, 11 Aug 2020 23:18:21 +0000
From:   benbjiang(蒋彪) 
        <benbjiang@...cent.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
CC:     Jiang Biao <benbjiang@...il.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "mgorman@...e.de" <mgorman@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Optimize dequeue_task_fair()(Internet mail)

Hi,

> On Aug 12, 2020, at 12:55 AM, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
> 
> On 11/08/2020 10:43, Jiang Biao wrote:
>> Similar optimization as what has been done in commit,
>> 7d148be69e3a(sched/fair: Optimize enqueue_task_fair())
>> 
>> dequeue_task_fair jumps to dequeue_throttle label when cfs_rq_of(se) is
>> throttled which means that se can't be NULL. We can move the label after
>> the if (!se) statement and remove the if(!se) statment as se is always
>> NULL when reaching this point.
>> 
>> Besides, trying to keep the same pattern with enqueue_task_fair can make
>> it more readable.
>> 
>> Signed-off-by: Jiang Biao <benbjiang@...cent.com>
>> ---
>> kernel/sched/fair.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 04fa8dbcfa4d..cbbeafdfa8b7 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5618,10 +5618,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>> 
>> 	}
>> 
>> -dequeue_throttle:
>> -	if (!se)
>> -		sub_nr_running(rq, 1);
>> +	/* At this point se is NULL and we are at root level*/
>> +	sub_nr_running(rq, 1);
>> 
>> +dequeue_throttle:
>> 	/* balance early to pull high priority tasks */
>> 	if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
>> 		rq->next_balance = jiffies;
> 
> There is already a similar patch in master.
> 
> 423d02e1463b - sched/fair: Optimize dequeue_task_fair() (2020-06-25 Peng
> Wang)
Indeed, my local repo has been outdated, sorry for the interruption. :)

Thx.
Regards,
Jiang