linux-kernel - Re: [RFC] Imprecise timers.

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Message-ID: <20080722055421.2023d261@infradead.org>
Date:	Tue, 22 Jul 2008 05:54:21 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Rene Herman <rene.herman@...access.nl>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [RFC] Imprecise timers.

On Tue, 22 Jul 2008 09:19:02 +0200
Rene Herman <rene.herman@...access.nl> wrote:

> On 22-07-08 05:02, David Woodhouse wrote:
> 
> > Many users of timers don't really care too much about exactly when
> > their timer fires -- and waking a CPU to satisfy such a timer is a
> > waste of power. This patch implements a 'range' timer which will
> > fire at a 'convenient' moment within given constraints.
> > 
> > It's implemented by a deferrable timer at the beginning of the
> > range, which will run some time later when the CPU happens to be
> > awake. And a non-deferrable timer at the hard deadline, to ensure
> > it really does happen by then.
> 
> Are there actually users for this (not just in theory)? The
> deferrable timer sort of sounds like all I'd ever want if I, as you
> say, wouldn't really care...

there's a few; mostly around hardware timeout..For example Stephen want
it for his drivers.

EXT3 journal flushing is another one where we can easily say 
"between 4 and 7 seconds" rather than "exactly at 5"


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