Re: [RFC] Imprecise timers.

From: Rene Herman
Date: Tue Jul 22 2008 - 10:02:41 EST

On 22-07-08 14:54, Arjan van de Ven wrote:

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

Hardware I've dealt with is (almost? can't remember anything else) exlusively minimal delays and as such this thing seemed like perhaps a bit over-apisized...

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

This a nice-ish example though. It might be considered necessary to make the current commit delay when set explicitly be the non-deferrable upper bound but almost none do I guess.

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