linux-kernel - Re: [RFC][PATCH 4/4] sched/fair: Optimize cgroup pick_next_task

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Date:	Tue, 19 Jun 2012 01:45:05 -0700
From:	Paul Turner <pjt@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, venki@...gle.com, efault@....de,
	rostedt@...dmis.org, glommer@...allels.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 4/4] sched/fair: Optimize cgroup pick_next_task_fair

On Fri, Jun 15, 2012 at 7:03 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2012-06-14 at 23:19 +0200, Peter Zijlstra wrote:
>> On Thu, 2012-06-14 at 15:29 +0200, Peter Zijlstra wrote:
>> > Since commit 2f36825b1 ("sched: Next buddy hint on sleep and preempt
>> > path") it is likely we pick a new task from the same cgroup, doing a put
>> > and then set on all intermediate entities is a waste of time, so try to
>> > avoid this.
>>
>> I just noticed put_prev_entity() also does the bandwidth enforcement
>> stuff, I think I just broke that. Will have a peek at fixing that
>> tomorrow or so.
>
> Damn, that's annoying, that wants to be done bottom-up, while we're now
> doing a top-down selection. pjt any sane ideas?

I'll have a look at this tomorrow, but I think this is fairly
immediately resolvable -- I don't see any immediate reason we need to
do  full enforcement here.  The only interesting thing we really need
to do in the put_path is the voluntary return of quota, which -- if we
need to do it -- we will get to do since that occurs iff the entity is
no longe runnable and actually getting a put().
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