linux-kernel - Re: [RFC][PATCH 1/7] sched: Replace post_schedule with a balance callback list

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Message-ID: <OF16420525.D7DCA965-ON48257E59.002BFF6E-48257E59.002E24BB@zte.com.cn>
Date:	Wed, 3 Jun 2015 16:24:05 +0800
From:	pang.xunlei@....com.cn
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	juri.lelli@...il.com, ktkhai@...allels.com,
	linux-kernel@...r.kernel.org, mingo@...e.hu, oleg@...hat.com,
	pang.xunlei@...aro.org, "Peter Zijlstra" <peterz@...radead.org>,
	rostedt@...dmis.org, umgwanakikbuti@...il.com
Subject: Re: [RFC][PATCH 1/7] sched: Replace post_schedule with a balance callback
 list

Hi Peter,

This may increase the overhead of schedule() a bit, as it will have 
more work to do.

check_class_changed():
        if (prev_class->switched_from)
                        prev_class->switched_from(rq, p);
                /* Possble rq->lock 'hole'.  */
                p->sched_class->switched_to(rq, p);

For above cases, why can't we just add a judgement in switched_to_fair() 
as follows:
if (rq != task_rq(p))
        return;

switched_to_rt() and switched_to_dl() already did the similar judgement.

Then the following operation is usually task_rq_unlock() or the like, 
seems no other harm with the old rq of p.

-Xunlei

Peter Zijlstra <peterz@...radead.org> wrote 2015-06-01 PM 09:58:19:
> [RFC][PATCH 1/7] sched: Replace post_schedule with a balance callback 
list
> 
> Generalize the post_schedule() stuff into a balance callback list.
> This allows us to more easily use it outside of schedule() and cross
> sched_class.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

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