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

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Message-ID: <20080809125447.GA13169@ucw.cz>
Date:	Sat, 9 Aug 2008 14:54:47 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	"arjan@...radead.org" <arjan@...radead.org>
Subject: Re: [RFC] Imprecise timers.

On Mon 2008-07-28 17:36:57, Pallipadi, Venkatesh wrote:
> 
> 
> >-----Original Message-----
> >From: linux-kernel-owner@...r.kernel.org
> >[mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of David
> >Woodhouse
> >Sent: Monday, July 21, 2008 8:03 PM
> >To: linux-kernel@...r.kernel.org
> >Cc: Thomas Gleixner; Ingo Molnar; arjan@...radead.org
> >Subject: [RFC] Imprecise timers.
> >
> >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.
> >
> 
> One concern I have is drivers using range_timers thinking that they need
> some upper bound, while all they need is a simple deferrable timer. With that
> we will have multiple timers waking up the CPU all the time (say, on
> different CPUs) problem again. Even without the timers waking up all

I don't get it. Who has timers that can be deferred forever? At that
point they may simply not set the timer at all, right?

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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