linux-kernel - Re: report a bug about sched

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Date:	Fri, 24 Jul 2009 17:24:30 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	sen wang <wangsen.linux@...il.com>
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

On Fri, 2009-07-24 at 23:07 +0800, sen wang wrote:
> 2009/7/24 Peter Zijlstra <peterz@...radead.org>:
> > On Fri, 2009-07-24 at 22:04 +0800, sen wang wrote:
> >
> >> just one question:
> >> if cpu is free and there is running state task, how you do?
> >> schedule the task up? or schedule idle task up?
> >
> > Well, when an RT group is over the bandwidth limit I don't consider them
> > runnable. Therefore, failing to find any other tasks, we run the idle
> > task.
> >
> 
> you havn't anwser the question: if cpu is free, should we  schedule the
> running state task or idle task?

It it not runnable because the group is over its limit.

> face the error and fix it! ok?

Please tone down and re-read the explanations I gave.

The throttle is an H-CBS services for RT task groups, meant to provide
isolation through a fixed resource guarantee.

Any process actually hitting the throttle means a miss configured system
-- unless its a temporary overload and you're able to deal with those.

The single group case is simply the trivial case thereof.

Your proposed change does not generalize to such a framework, and while
it might work with the current code, it doesn't serve a use-case
considered in this architecture and will render the interface
inconsistent.

Furthermore, future work in this area will not be able to support your
changed semantics in a sane fashion.

I've yet to see any coherent explanation of your problem, and quite
frankly I find your attitude offensive.

As you say, Linux is an open-source effort, and you're free to do with
your copy as you see fit (provided you stick to the rules stipulated by
the GPLv2). However as co-maintainer of the mainline scheduler I see no
reason to entertain your change, nor for that matter to continue this
discussion.

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