Subject: Re: massive_intr on CFS, BFS, and EDF
From: Peter Zijlstra <peterz@infradead.org>
To: Chris Friesen <cfriesen@nortel.com>
Cc: Michael Trimarchi <trimarchi@gandalf.sssup.it>,
       sat <takeuchi_satoru@jp.fujitsu.com>,
       lkml <linux-kernel@vger.kernel.org>, Con Kolivas <kernel@kolivas.org>,
       Ingo Molnar <mingo@elte.hu>, Raistlin <raistlin@linux.it>
In-Reply-To: <4ABD36CE.3080400@nortel.com>
References: <4ABC068A.6070704@jp.fujitsu.com>
	 <4ABCEABC.4050200@gandalf.sssup.it>  <4ABD36CE.3080400@nortel.com>
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Date: Sat, 26 Sep 2009 00:37:38 +0200
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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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