cpufreqd as standard install?

Matthew Garrett mjg59 at srcf.ucam.org
Thu Mar 8 16:10:48 UTC 2012

On Thu, Mar 08, 2012 at 11:03:42AM -0500, Phillip Susi wrote:
> On 3/8/2012 9:47 AM, Matthew Garrett wrote:
> >This is (broadly speaking) untrue. There's a bunch of fixed costs that a
> >naive P=IVĀ² doesn't take into account. Assuming a fixed amount of work,
> >race to idle is almost always the most power efficient strategy.
> What fixed costs?  If you spend 5 seconds working at full throttle
> and consuming 100 watts, and then the next 25 seconds in deep C6
> consuming 0 watts, you've spent 500 joules of energy.  If you
> instead spend 10 seconds working at half frequency, consuming only
> 30 watts, then the next 20 seconds in deep C6, you've only spent 300
> joules for the same work.  When you factor in the typical increased
> execution efficiency you get at the lower frequencies, you probably
> could finish that work in only 9 seconds, cutting the energy
> expenditure down to 270 joules.

Yes, if those are the actual power figures. But they're typically not 
going to be.

Matthew Garrett | mjg59 at srcf.ucam.org

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