linux-kernel - Re: [RFC] Dynamic Tick and Deferrable Timer Support

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Date:	Sat, 7 Feb 2009 10:20:49 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	john stultz <johnstul@...ibm.com>
Cc:	Jon Hunter <jon-hunter@...com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] Dynamic Tick and Deferrable Timer Support

> > So what I was proposing is that for devices that have timers that would 
> > allow you to sleep beyond ~2.15 seconds (current max imposed by the 
> > clockevent_delta2ns function), why not increase the dynamic range (make 
> > this a 64-bit variable) or base (ie. from nanoseconds to milliseconds) 
> > to permit longer sleep times for devices that can support them? This 
> > should not have any negative impact on devices that cannot support such 
> > long sleep times.
> 
> No objection to max_delta_ns being increased, but whatever code manages
> it will probably need to query the timekeeping core in some fashion to
> make sure the timer hardware max isn't larger then the clocksource
> hardware max. I've provided a rough sketch at what the timekeeping code
> would probably look like below.
> 
> > So far I have not encountered any issues with doing this. Let me know if 
> > this does or does not address your concerns.
> 
> There may be some other issues here, such as NTP over-correction issues
> (for instance: ntp trying to correct for a 1us offset over the next
> second, but ends up applying it for 10 seconds) if we defer for a really
> long time. But at that point, we might as well suspend to ram, like the
> OLPC does.

Well, there's still some way to go before auto-sleep is
possible. android can do that, afaict, but on pc it is quite far away.


-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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