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

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Message-ID: <BANLkTimFv59s1B4dPsrWQGdH+FO-omcXyA@mail.gmail.com>
Date:	Tue, 24 May 2011 23:04:44 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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, May 24, 2011 at 10:46 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 2011-05-24 at 22:33 +0800, Hillf Danton wrote:
>> On Tue, May 24, 2011 at 10:24 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>> > 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.
>> >
>> If it is one of the current principles in RT schedule, the patch has
>> to be dropped.
>>
>
> Yes, that is the definition of FIFO (First In First Out). The tasks that
> get to the CPU first run till they voluntarily schedule away, or are
> preempted by an even high priority task. Tasks of the same priority must
> wait till the previous task has finished.
>

Though I dont know who is the author of pusher, I like it, and the comments
related to it. The patch is a try to take advantage of pusher to
relive starvation
a bit, but failed.

thanks all comments.

Hillf
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