Date: Wed, 16 Jan 2008 15:27:19 +0000 From: "Igor Mozolevsky" <igor@hybrid-lab.co.uk> To: "John Baldwin" <jhb@freebsd.org> Cc: njl@freebsd.org, bruno@freebsd.org, Stefan Lambrev <stefan.lambrev@moneybookers.com>, freebsd-current@freebsd.org, =?ISO-8859-1?Q?Dag-Erling_Sm=F8rgrav?= <des@des.no>, Maxim Sobolev <sobomax@digifonica.com> Subject: Re: powerd adaptive mode latching Message-ID: <a2b6592c0801160727n106d8a69tc9d1068a062bf837@mail.gmail.com> In-Reply-To: <200801161009.55401.jhb@freebsd.org> References: <a2b6592c0801110351l382959ffh1d55f2bcd2e6ca1b@mail.gmail.com> <a2b6592c0801111119r148d3697hf75a59b7bf74d540@mail.gmail.com> <478930D2.90806@digifonica.com> <200801161009.55401.jhb@freebsd.org>
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On 16/01/2008, John Baldwin <jhb@freebsd.org> wrote: > On Saturday 12 January 2008 04:27:46 pm Maxim Sobolev wrote: > > I wonder if somebody did measurement of power consumption with powerd > > and without it on typical tasks. There is very interesting idea in the > > last issue of ACM Queue that it might be much more beneficial to run CPU > > at the full speed and then switch it to low-power mode as soon as > > possible in the idle loop than to run longer at reduced speed for a > > longer period of time. > > I haven't done hard tests, but even with C3 enabled on my laptop I find that > anecdotally I get longer battey life with powerd enabled. That could be something to do with the rate of throttling of powerd; I can't remember how long it was exactly, but under the default setting it would take powerd 9s to go from 100MHz to full clock speed on my T43p, by which time, I would suspect most of hard tasks would be done and the clock would be dropped back to something minuscule. Baring in mind that the power consumption vs clock rate is not a linear relationship in most cases. I think the only way we could get a significant benefit from low CPU clock in idle loop without the powerd would be if/when the kernel becomes tick-less (which I think is a pretty cool idea)... Igor
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