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SubjectRe: CPU throttling??
On Mon, Feb 03, 2003 at 01:14:18PM -0800, you [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.

Interesting.

So, what sw does one need for this CPU C state? Which kernels support it /
which patches are needed? 2.5 only?

Also, which CPUs support it? Am I out of luck with my measly 1.4 Celeron
Tualatin?

So far I've only been doing "Make CPU Idle calls when idle", which I gather
is far from optimal?


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