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Subject: RE: CPU throttling??
From: Seamus <assembly@gofree.indigo.ie>
To: "Grover, Andrew" <andrew.grover@intel.com>
Cc: Dave Jones <davej@codemonkey.org.uk>, Valdis.Kletnieks@vt.edu,
       John Bradford <john@grabjohn.com>, linux-kernel@vger.kernel.org
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On Mon, 2003-02-03 at 21:14, Grover, Andrew wrote:
> > From: Dave Jones [mailto:davej@codemonkey.org.uk] 
> > Valdis.Kletnieks@vt.edu wrote:
> > 
> >  > It's conceivable that a CPU halted at 1.2Gz takes less 
> > power than one
> >  > at 1.6Gz - anybody have any actual data on this?  
> > Alternately phrased,
> >  > does CPU throttling save power over and above what the halt does?
> > 
> > Given that most decent implementations scale voltage as well as
> > frequency, yes, a lower speed will save more power.
> 
> You save the most power when the CPU is at the lowest voltage level, and
> in the deepest CPU sleep state (aka CPU C state).
> 
> Throttling offers a linear power/perf tradeoff if your system doesn't
> have C state support (or if you aren't using it) but really it is
> preferable to keep the CPU at its nominal speed, get the work done
> sooner, and start sleeping right away. The quote above makes it sound
> like the voltage is scaled when throttling, and that isn't accurate -
> voltage is scaled when sleeping (to counteract leakage current), at
> least on modern Intel mobile processors.
> 
> Valdis, you may want to try compiling in ACPI and ACPI Processor support
> in 2.5.latest and see what happens to your battery life (if you haven't
> tried already). (A caveat - ACPI still doesn't work for everyone, but if
> it does, you should see a power savings.)
> 
> Regards -- Andy

Hmmm, it seems most of these apply to mobile processors.
I'm using AMD 1.4 Athlon Thunderbird on a desktop, as you know my
processor was the one before release low power AMD XP processors.
It uses a savage amount of power, and operates well into 60 and 70
degrees celcius.

I'm not a big linux head, can someone through me an ACPI link, related
to this issue of CPU C state?

One other thing, apart from saving power on CPU and hard-disk (via
hdparm) is there anything else I can look into ? something worthy
though.

Thanks,

Seamus

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