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From:   =?iso-2022-jp?B?YmVuYmppYW5nKBskQj5VSTcbKEIp?= 
        <benbjiang@tencent.com>
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
CC:     Jiang Biao <benbjiang@gmail.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
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        "bsegall@google.com" <bsegall@google.com>,
        "mgorman@suse.de" <mgorman@suse.de>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched/fair: Optimize dequeue_task_fair()(Internet mail)
Thread-Topic: [PATCH] sched/fair: Optimize dequeue_task_fair()(Internet mail)
Thread-Index: AQHWb7uHIOwUFikfVEWDShzE3PLAcakymr+AgABqtoA=
Date:   Tue, 11 Aug 2020 23:18:21 +0000
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 <9a2ddb2d-4c9a-a85d-cba2-0956b6d953c0@arm.com>
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Hi,

> On Aug 12, 2020, at 12:55 AM, Dietmar Eggemann <dietmar.eggemann@arm.com>=
 wrote:
>=20
> 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())
>>=20
>> 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.
>>=20
>> Besides, trying to keep the same pattern with enqueue_task_fair can make
>> it more readable.
>>=20
>> Signed-off-by: Jiang Biao <benbjiang@tencent.com>
>> ---
>> kernel/sched/fair.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>=20
>> 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, str=
uct task_struct *p, int flags)
>>=20
>> 	}
>>=20
>> -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);
>>=20
>> +dequeue_throttle:
>> 	/* balance early to pull high priority tasks */
>> 	if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
>> 		rq->next_balance =3D jiffies;
>=20
> There is already a similar patch in master.
>=20
> 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Indeed, my local repo has been outdated, sorry for the interruption.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