linux-kernel - Re: report a bug about sched

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Message-ID: <20090724072826.4c35bc2a@infradead.org>
Date:	Fri, 24 Jul 2009 07:28:26 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	sen wang <wangsen.linux@...il.com>
Cc:	mingo@...e.hu, akpm@...ux-foundation.org, kernel@...ivas.org,
	npiggin@...e.de, linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: report a bug about sched_rt

On Fri, 24 Jul 2009 18:57:35 +0800
sen wang <wangsen.linux@...il.com> wrote:

> I find something is wrong about sched_rt.
> 
>  when I am debugging my system with rt_bandwidth_enabled, there is a
> running realtime FIFO task in the sched_rt running queue and
>  the fair running queue is empty.  I found the idle task will be
> scheduled up when the running task still lie in the  sched_rt running
> queue!
> 
> this will happen when rt runqueue passed it's rt_bandwidth_enabled
> runtime,then the scheduler choose the idle task instead of realtime
> FIFO task.
> 
> the reason lie in: when scheduler try to pick up a realtime FIFO task,
> it will check if rt_throttled is enabled,
> if so, it'll return and try fair queue but it is empty, then it come
> to the sched_idle class.
> 
> I don't think it reasonable, we should give the realtime FIFO task the
> chance, even when rt runqueue passed it's runtime.
> because it is cpu's free time.


sounds like a good power limiting feature...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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