linux-kernel - Re: report a bug about sched

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Date:	Fri, 24 Jul 2009 21:26:42 +0800
From:	sen wang <wangsen.linux@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...e.hu, akpm@...ux-foundation.org, kernel@...ivas.org,
	npiggin@...e.de, arjan@...radead.org,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: report a bug about sched_rt

don't tell me what theory. don't be so doctrinairism! OK?
If cpu is free and there is a running state task,how can you scdedule
idle task up?
I tell you again:we are not talking about a bandwidth of 100% for RT!
Bug lies in the bandwidth of (100- X)%.(X<100)
even in the time of 100-X,if there is a rt task, you should not idle()
the system.


2009/7/24 Peter Zijlstra <peterz@...radead.org>:
> Don't top post -- again!
>
> On Fri, 2009-07-24 at 21:04 +0800, sen wang wrote:
>> Linux is used in many fieldes. SCHED_OTHER tasks is important to
>> embedded system.
>
> Irrelevant.
>
>> if there is a running state task（a realtime task）, how can we
>> shcedule the idle task up?
>
> Because it ran out of bandwidth.
>
>> It is ridiculous！
>>
>> since the throttle has a bug, why not fix it?
>
> It doesn't have a bug, therefore I won't fix it.
>
> The throttle limits the RT tasks to a bandwidth w of u/p.
> Since real-time scheduling is about determinism a maximum bandwidth
> larger than the minimum bandwidth specified by w is useless since it
> cannot be relied upon.
>
> Therefore we don't run RT tasks beyond their bandwidth limit.
>
> Go read up on scheduling theory.
>
> Now you might want a bandwidth of 100% for your RT application (not
> something I can recommend for the overall health of your machine) in
> which case you're free to change this setting:
>
>  echo -1 > /proc/sys/kernel/sched_rt_runtime_us
>
> Should do that for you. Also read:
>
>  Documentation/scheduler/sched-rt-group.txt
>
>
>
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