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

On Sat, May 09, 2009 at 01:56:09PM +0800, bill lam wrote:
> > 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.
> >
> >
>
> Thanks all for confirmation. Since I only have a desktop, no
> notebook/netbook ;-( it is somehow difficult to verify the
> improvement. I now lock the cpu frequency to 1.1GHZ (half of the
> original 2.1G).
>
> Less heat means less power consumption, I guess someone suggested,
> (I'm not sure that's why I asked for advise), that it takes more time
> to complete the job at lower frequency so that actual power
> consumption will in some case increase.

It's more efficient to run at full speed and then let the CPU halt (you
have to have a tickless system though) [1-4]. Decreasing power consumption
of sychronous processors is a really hard problem [5-7]. But anyhow I'm not
a physicist or electrical engineer.
 
Regards,
Matthias-Christian

[1] http://www.codon.org.uk/~mjg59/power/good_practices.html
[2] https://www.redhat.com/docs/wp/performancetuning/Power_Management_Guide.pdf
[3] http://www.ncsu.edu/wcae/ISCA2007/p52-suarez.pdf
[4] http://lists.us.dell.com/pipermail/linux-poweredge/2007-December/033900.html
[5] http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=3276&p=6
[6] http://patmos2001.eivd.ch/program/Repro%5CArt_10_1.pdf
[7] http://async.org.uk/ukasyncforum14/forum14-papers/forum14-moore.pdf
[8] http://www.fulcrummicro.com/press_archives/edn_03-0501.pdf
Received on Sat May 09 2009 - 08:57:14 UTC