linux-kernel - Re: [RFC 8/12][PATCH] SCHED_DEADLINE: wait next instance syscall added.

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Date:	Wed, 13 Jan 2010 10:33:04 +0100
From:	Raistlin <raistlin@...ux.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	michael trimarchi <michael@...dence.eu.com>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	Chris Friesen <cfriesen@...tel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Henrik Austad <henrik@...tad.us>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Sven-Thorsten Dietrich <sven@...bigcorporation.com>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
	"giuseppe.lipari" <giuseppe.lipari@...up.it>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [RFC 8/12][PATCH] SCHED_DEADLINE: wait next instance syscall
 added.

On Mon, 2009-12-28 at 15:30 +0100, Peter Zijlstra wrote:
> > However, for SCHED_DEADLINE tasks, it should be the call with which each
> > job closes its current instance. In fact, in this case, the task is put to
> > sleep and, when it wakes up, the scheduler is informed that a new job
> > arrived, saving the overhead that usually comes with a task activation
> > to enforce maximum task bandwidth.
> 
> The changelog suggests (and a very brief looks seems to confirm) that
> this code could be much smaller by using hrtimer_nanosleep().
> 
> The implementation as presented seems to only call ->wait_interval()
> when the timer arms, which seems like a bug, we should always call it,
> regardless of whether we're on a period boundary.
> 
Ok, thanks, I'll look carefully at that! The current code is an attempt
of mine to replicate the behaviour of clock_nanosleep, but you're
definitely right here, it can be done much better.

Thanks and regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa  (Italy)

http://blog.linux.it/raistlin / raistlin@...ga.net /
dario.faggioli@...ber.org

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