linux-kernel - Re: massive_intr on CFS, BFS, and EDF

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Date:	Sat, 26 Sep 2009 00:37:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	Michael Trimarchi <trimarchi@...dalf.sssup.it>,
	sat <takeuchi_satoru@...fujitsu.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Con Kolivas <kernel@...ivas.org>, Ingo Molnar <mingo@...e.hu>,
	Raistlin <raistlin@...ux.it>
Subject: Re: massive_intr on CFS, BFS, and EDF

On Fri, 2009-09-25 at 15:31 -0600, Chris Friesen wrote:
> On 09/25/2009 10:07 AM, Michael Trimarchi wrote:
> > It is important to note that
> > the expected behavior of an edf scheduler is *not* a fair one. It has to
> > do its best to guarantee the deadlines of the admitted tasks.
> 
> Do you allow oversubscription with EDF?  It would seem so based on these
> results.  Would it maybe make sense to disallow oversubscription, or
> make it an option?

afaiu he doesn't, he simply splits the task's wcet between parent and
child and (intends?) to feed back on child exit.

> If you have massive oversubscription with EDF, what is the design
> intent?  Do you try to meet the goals on as many tasks as possible,
> while the oversubscribed tasks get nothing?

oversubscribing edf isn't in general recommended, iirc u>1 gives
unbounded latencies with edf.

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