Re: [dwm] [OT] frequency scaling and power consumption

From: <>
Date: Fri, 8 May 2009 16:23:52 +0100 (BST)

> On Fri, May 8, 2009 at 9:08 AM, bill lam <> wrote:
>> BIOS support choosing a smaller multipliers to reduce cpu frequency.
>> linux also supports frequency scaling such powernowd. Some google
>> page said cpu throttling can not reduce power consumption. My
>> experience is that it seems to lower temperature. If it can also
>> reduce power consumption, I'm willing to save money by running cpu at
>> half of its current frequency. Any idea.
> My understanding is that power usage scales nonlinearly with CPU
> frequency, and in particular having twice the frequency doesn't
> require quite as much as double the power. So IF your OS can put your
> PC into proper "sleep" states whent here's nothing to do (and that's
> the big IF), the PC will use less energy in total by running at full
> speed when you have work to do and then going into a sleep state
> rather than taking twice as long to do the work at half the frequency.
> So I'd expect you'd probably get more "energy usage reduction" from
> getting rid of any services/device drivers/etc that stop the PC going
> to sleep than from manually reducing the frequency. (If you're using
> Linux, PowerTOP (
> ) is an attempt to provide a way to at least see what's causing
> wake-ups, even if it doesn't necessarily show how to solve them.)
>> --

Personally I have noticed that locking my laptops scaling CPU to the
lowest frequency does give quite a noticeable improvement to the battery
life, around an extra hour on top of the usual 4~ hours and reduces the
temperature enough to make the fan shut off . Just enabling on-demand
scaling didn't help much as it would scale up to full frequency far to
often. Even with the CPU locked in lo frequency mode it almost never lags.
Received on Fri May 08 2009 - 15:23:52 UTC

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