linux-kernel - Re: [PATCH] sched: remove starvation in check_preempt_equal

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Message-ID: <1306247058.1465.66.camel@gandalf.stny.rr.com>
Date:	Tue, 24 May 2011 10:24:18 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Mike Galbraith <efault@....de>,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH] sched: remove starvation in check_preempt_equal_prio()

On Tue, 2011-05-24 at 22:01 +0800, Hillf Danton wrote:
> On Tue, May 24, 2011 at 9:47 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Tue, 2011-05-24 at 21:34 +0800, Hillf Danton wrote:
> >> If there are pushable tasks and they are high enough in priority, in which
> >> case task p is covered, the current could keep holding its CPU.
> >
> > -ENOPARSE..
> >
> 
> Here the priority is same, then pushing task p off has little difference from
> pushing any other pushable.

If task p is currently running and is a FIFO task, you do not push it
off for another task of same prio.

> 
> >> Even if current task has to release its CPU, requeuing task p could result in
> >> starvation of tasks that are of same priority and have been waiting on RQ for
> >> a couple of hours:/
> >
> > Starvation of the same priority tasks is a perfectly valid situation for
> > SCHED_FIFO, also, your changelog fails to mention what you propose to do
> > about it.
> >
> I did get curr requeued, and task_woken_rt() could do what I want.
> 
> If you change ENOPARSE to PARSE, I will change task_woken_rt accordingly.

I'm not sure I can change to PARSE yet.

-- Steve


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