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SubjectRe: CPU throttling??
On Mon, Feb 03, 2003 at 01:14:18PM -0800, Grover, Andrew wrote:

> 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.

Most (all?[1]) other modern x86 mobile processors behave the way I mentioned.
AMD Powernow (K6 and K7), VIA longhaul/powersaver all have optimal voltages
they can be run at when clocked to different speeds. By way of example, a table from
my mobile athlon..

FID: 0x12 (4.0x [532MHz]) VID: 0x13 (1.200V)
FID: 0x4 (5.0x [665MHz]) VID: 0x13 (1.200V)
FID: 0x6 (6.0x [798MHz]) VID: 0x13 (1.200V)
FID: 0xa (8.0x [1064MHz]) VID: 0xd (1.350V)
FID: 0xf (10.5x [1396MHz]) VID: 0x9 (1.550V)

Sure I *could* run that at 523MHz and still pump 1.550V into it,
but why would I want to do that ?

Dave

[1] Unsure about the crusoe.

--
| Dave Jones. http://www.codemonkey.org.uk
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