Messages in this thread | | | Date | Tue, 4 Feb 2003 00:31:05 +0200 | From | Ville Herva <> | Subject | Re: CPU throttling?? |
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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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