Re: 2.6.15-ck1

[Adam Belay <ambx1@neo.rr.com>]

On Wed, Jan 04, 2006 at 02:05:54PM -0500, Dave Jones wrote:
> On Wed, Jan 04, 2006 at 12:00:00PM +1100, Con Kolivas wrote:
>  >  +2.6.15-dynticks-060101.patch
>  >  +dynticks-disable_smp_config.patch
>  > Latest version of the dynticks patch. This is proving stable and effective on 
>  > virtually all uniprocessor machines and will benefit systems that desire 
>  > power savings. SMP kernels (even on UP machines) still misbehave so this 
>  > config option is not available by default for this stable kernel.
> 
> I've been curious for some time if this would actually show any measurable
> power savings. So I hooked up my laptop to a gizmo[1] that shows how much
> power is being sucked.
> 
> both before, and after, it shows my laptop when idle is pulling 21W.
> So either the savings here are <1W (My device can't measure more accurately
> than a single watt), or this isn't actually buying us anything at all, or
> something needs tuning.
> 
> 		Dave

I've done quite a bit of testing with dynticks and various c-state strategies.
On my thinkpad T42, dynticks can save about .5 W (as read from the ACPI battery
interface, but hey it's a good ballpark measurement).  This is when compared to
250HZ and the stock ACPI c-state code.  Both tests were running at the lowest
processor frequency (600 MHZ).  The savings were much greater when running at
1.7 GHZ or when comparing to a HZ value of 1000.  Also the advantage was closer
to 1 W when X was not running.

It might be possible to do even a little better.  Currently, I'm developing a
new ACPI idle policy that tries to take advantage of the long time we may
be able to spend in a C3 state.

Thanks,
Adam