linux-kernel - Re: [sched/rt] Optimization of function pull_rt

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Message-ID: <1334773976.28106.49.camel@gandalf.stny.rr.com>
Date:	Wed, 18 Apr 2012 14:32:56 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [sched/rt] Optimization of function pull_rt_task()

On Mon, 2012-04-16 at 12:06 -0400, Steven Rostedt wrote:
> On Sun, 2012-04-15 at 23:45 +0400, Kirill Tkhai wrote:
> > The condition (src_rq->rt.rt_nr_running) is weak because it doesn't
> > consider the cases when src_rq has only processes bound to it (when
> > single cpu is allowed). It may be running kernel thread like
> > migration/x etc.
> > 
> > So it's better to use more stronger condition which is able to exclude
> > above conditions. The function has_pushable_tasks() complitely does
> > this. A task may be pullable for another cpu rq only if he is pushable
> > for his own queue.
> 
> I considered this before, and for some reason I never did the change.
> I'll have to think about it. It seems like this would be the obvious
> case, but I think there was something not so obvious that caused issues.
> But I don't remember what it was.
> 
> I'll have to rethink this again.

I can't find anything wrong with this change. Maybe things change, or I
was thinking of another change.

I'll apply it and start running my tests against it.

Thanks!

-- Steve

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