linux-kernel - Re: IO scheduler based IO Controller V2

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Date:	Sat, 09 May 2009 11:22:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Andrea Righi <righi.andrea@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, nauman@...gle.com,
	dpshah@...gle.com, lizf@...fujitsu.com, mikew@...gle.com,
	fchecconi@...il.com, paolo.valente@...more.it,
	jens.axboe@...cle.com, ryov@...inux.co.jp, fernando@....ntt.co.jp,
	s-uchida@...jp.nec.com, taka@...inux.co.jp,
	guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, agk@...hat.com,
	dm-devel@...hat.com, snitzer@...hat.com, m-ikeda@...jp.nec.com
Subject: Re: IO scheduler based IO Controller V2

On Fri, 2009-05-08 at 17:56 -0400, Vivek Goyal wrote:
>   So, we shall have to come up with something better, I think Dhaval was
>   implementing upper limit for cpu controller. May be PeterZ and Dhaval can
>   give us some pointers how did they manage to implement both proportional
>   and max bw control with the help of a single tree while maintaining the
>   notion of prio with-in cgroup.

We don't do max bandwidth control in the SCHED_OTHER bits as I oppose to
making it non work conserving.

SCHED_FIFO/RR do constant bandwidth things and are always scheduled in
favour of SCHED_OTHER. 

That is, we provide a minimum bandwidth for real-time tasks, but since
having a maximum higher than the minimum is useless since one cannot
rely on it (non deterministic) we put max = min.

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