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

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Date:	Tue, 24 May 2011 22:01:09 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mike Galbraith <efault@....de>,
	Yong Zhang <yong.zhang0@...il.com>
Subject: Re: [PATCH] sched: remove starvation in check_preempt_equal_prio()

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.

>> 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.

thanks
          Hillf
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