linux-kernel - Re: [PATCH] sched: change pull_rt_task() to decrease time waiting on runqueue

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Message-ID: <BANLkTingJ7s5SR+QWuE=_P5tcbuaB_bEwQ@mail.gmail.com>
Date:	Wed, 18 May 2011 22:54:55 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH] sched: change pull_rt_task() to decrease time waiting on runqueue

On Wed, May 18, 2011 at 9:27 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Wed, 2011-05-18 at 20:57 +0800, Hillf Danton wrote:
>> It is changed to be pushing RT task, then the pushable tasks on other
>> runqueus have chances to reach all CPUS whose runqueus are lower in
>> priority, which is not covered by pull since only one runqueue is
>> considered in pull for accepting tasks on other runqueues. Thus the
>> time of pushable tasks waiting on runqueue could be decreased.
>
> Do you have numbers and test cases for this? Or at least traces that
> show how this helps?
>
> Basically, you are saying that we want to iterate over all CPUs and have
> them go through the algorithm of searching for rqs that they can push
> to. But we already know that our run queue has dropped priority.
>
> I'm not fully understanding the benefit of this patch.
>

Hi Steve

In short, if there are pushable tasks and if there are RQs,
NOT LIMITED TO our RQ, in lower priority, tasks should be pushed to
RQs as many as we could.

Hillf
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