linux-kernel - Re: [PATCH 01/13] sched: Add 3 new scheduler syscalls to support an extended scheduling parameters ABI

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Message-ID: <20140121154603.GF3694@twins.programming.kicks-ass.net>
Date:	Tue, 21 Jan 2014 16:46:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michael Kerrisk <mtk.manpages@...il.com>
Cc:	Dario Faggioli <raistlin@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, rostedt@...dmis.org,
	Oleg Nesterov <oleg@...hat.com>, fweisbec@...il.com,
	darren@...art.com, johan.eker@...csson.com, p.faure@...tech.ch,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	claudio@...dence.eu.com, michael@...rulasolutions.com,
	fchecconi@...il.com, tommaso.cucinotta@...up.it,
	juri.lelli@...il.com, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	insop.song@...il.com, liming.wang@...driver.com, jkacur@...hat.com
Subject: Re: [PATCH 01/13] sched: Add 3 new scheduler syscalls to support an
 extended scheduling parameters ABI

On Tue, Jan 21, 2014 at 04:38:51PM +0100, Peter Zijlstra wrote:
>     SCHED_DEADLINE: Sporadic task model deadline scheduling
> 	SCHED_DEADLINE is an implementation of GEDF (Global Earliest
> 	Deadline First) with additional CBS (Constant Bandwidth Server).

We might want to re-word that to:

	SCHED_DEADLINE currently is an implementation of GEDF, however
	any policy that correctly schedules the sporadic task model is
	a valid implementation.

To make sure we should not rely on the actual implementation; there's
many possible algorithms to schedule the sporadic task model.

> 	The CBS guarantees that tasks that over-run their specified
> 	budget are throttled and do not affect the correct performance
> 	of other SCHED_DEADLINE tasks.
> 
> 	SCHED_DEADLINE tasks will fail FORK(2) with -EAGAIN
> 
> 	Setting SCHED_DEADLINE can fail with -EINVAL when admission
> 	control tests fail.
> 
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