Subject: Re: [RFC 8/12][PATCH] SCHED_DEADLINE: wait next instance syscall
 added.
From: Peter Zijlstra <peterz@infradead.org>
To: Raistlin <raistlin@linux.it>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       michael trimarchi <michael@evidence.eu.com>,
       Fabio Checconi <fabio@gandalf.sssup.it>, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Dhaval Giani <dhaval.giani@gmail.com>,
       Johan Eker <johan.eker@ericsson.com>, "p.faure" <p.faure@akatech.ch>,
       Chris Friesen <cfriesen@nortel.com>,
       Steven Rostedt <rostedt@goodmis.org>, Henrik Austad <henrik@austad.us>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Darren Hart <darren@dvhart.com>,
       Sven-Thorsten Dietrich <sven@thebigcorporation.com>,
       Bjoern Brandenburg <bbb@cs.unc.edu>,
       Tommaso Cucinotta <tommaso.cucinotta@sssup.it>,
       "giuseppe.lipari" <giuseppe.lipari@sssup.it>,
       Juri Lelli <juri.lelli@gmail.com>
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	 <1255707898.6228.463.camel@Palantir>
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Date: Mon, 28 Dec 2009 15:30:01 +0100
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On Fri, 2009-10-16 at 17:44 +0200, Raistlin wrote:
> This commit introduces another new SCHED_DEADLINE related syscall. It is
> called sched_wait_interval() and it has close-to-clock_nanosleep semantic.
> 
> 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.

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