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Subject: Re: [PATCH] Dynamic tick for x86 version 050610-1
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Tony Lindgren <tony@atomide.com>
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Date: Tue, 21 Jun 2005 11:49:20 +1000
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On Mon, 2005-06-20 at 18:28 -0700, Tony Lindgren wrote:
> On Sat, Jun 18, 2005 at 04:30:32PM +1000, Benjamin Herrenschmidt wrote:
> > 
> > > I'm try to port it powerpc, Here is a patch.
> > > 
> > >  Port Dynamic Tick Timer to new platform is easy. :)
> > >   1) Find the reprogram timer interface.
> > >   2) do a hook in the idle function.
> > > 
> > > That worked on my PowerBookG4 12'.
> 
> Cool :)
> 
> > Did you get a measurable gain on power consumption ?
> > 
> > Last time I toyed with this, I didn't.
> 
> Just dyntick alone probably does not do much for power savings. The
> trick is to figure out what all can be turned off for the longer idle
> periods. And try to make the idle periods longer by cutting down on
> polling.

I would have expected it to actually do increase savings due to avoiding
the cost of bringing the CPU back from deep NAP mode too often. It's
possible that my previous experiments were bogus in fact. It would be
very useful to have some statistics on how long we _actually_ sleep, I
supspect things like the network stack with all it's slow timer all
kicking at slightly different times for example are screwing us up a
little bit.

Ben.