Messages in this thread | | | Date | Wed, 4 Jan 2006 17:57:31 -0800 | From | Tony Lindgren <> | Subject | Re: 2.6.15-ck1 |
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* Con Kolivas <kernel@kolivas.org> [060104 15:23]: > On Thursday 05 January 2006 06:57, Dave Jones wrote: > > 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. > > > > Ah interesting. It needs to be totally idle for a period of time before > > anything starts to happen at all. After about a minute of doing nothing, > > it started to fluctuate once a second 20,21,19,20,19,20,18,21,19,20,22 > > etc.. > > > > Goes no lower than 18W, and only occasionally peaks above the old idle > > power usage. Not bad at all. > > > > Causing any activity at all puts it back to the 'have to wait a while > > for things to start happening' state again. > > Thanks for testing it. Indeed skipping the ticks alone does not really save > any significant amount of power. The real chance for power savings comes from > using this period for smarter C state programming. The other thing as you've > noticed is that timers need to be curbed or minimised to get the maximum > benefit and the ondemand governor alone, which unfortunately shows up as > something not obvious in timertop, polls at 140HZ itself - fiddling with > ondemand/ settings in sys can drop this but slows the rate at which it > adapts.
Device specific power states will help with getting power savings too.
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