linux-kernel - Re: [PATCH 4/8] sched: clean up move_task() and move_one

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Date:	Wed, 20 Mar 2013 22:42:52 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] sched: clean up move_task() and move_one_task()

2013/3/20 Peter Zijlstra <peterz@...radead.org>:
> On Wed, 2013-03-20 at 16:33 +0900, Joonsoo Kim wrote:
>
>> > Right, so I'm not so taken with this one. The whole load stuff really
>> > is a balance heuristic that's part of move_tasks(), move_one_task()
>> > really doesn't care about that.
>> >
>> > So why did you include it? Purely so you didn't have to re-order the
>> > tests? I don't see any reason not to flip a tests around.
>>
>> I think that I'm not fully understand what you are concerning, because of
>> my poor English. If possible, please elaborate on a problem in more detail.
>
> OK, so your initial Changelog said it wanted to remove some code
> duplication between move_tasks() and move_one_task(); but then you put
> in the load heuristics and add a boolean argument to only enable those
> for move_tasks() -- so clearly that wasn't duplicated.
>
> So why move that code.. I proposed that this was due a reluctance to
> re-arrange the various tests that stop the migration from happening.
>
> Now you say:
>
>> ... Just moving up can_migrate_task() above
>> load evaluation code may raise side effect, because can_migrate_task() have
>> other checking which is 'cache hottness'. I don't want a side effect. So
>> embedding load evaluation to can_migrate_task() and re-order checking and
>> makes load evaluation disabled for move_one_task().
>
> Which pretty much affirms this. However I also said that I don't think
> the order really matters that much; each test will cancel the migration
> of this task; the order of these tests seem immaterial.
>
>> If your recommandation is to move up can_mirate_task() above
>> load evaluation code, yes, I can, and will do that. :)
>
> I would actually propose moving the throttled test into
> can_migrate_task() and leave it at that.

Okay. I will do that in next spin.

Thanks!!

>
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