Messages in this thread |  | | From | "H. Peter Anvin" <> | Subject | Re: rdtsc to mili secs? | Date | 10 Nov 2000 15:00:08 -0800 |
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Followup to: <200011102223.XAA04330@cave.bitwizard.nl> By author: R.E.Wolff@BitWizard.nl (Rogier Wolff) In newsgroup: linux.dev.kernel > > > > Intel PIIX-based systems will do duty-cycle throttling, for example. > > What's this "duty cycle throtteling"? Some people seem to think this > refers to changing the duty cycle on the clock, and thereby saving > power. I think it doesn't save any power if you do it that way. You > are referring to the duty cycle on a "stpclk" signal, right? >
Yes. The clock to the CPU isn't actually halted, but the STPCLK input is pulsed, usually at 4 kHz, with some specific duty cycle.
It saves power roughly linearly with the duty cycle, minus some overhead. It tends to be used mostly for thermal protection; if all you have is duty cycle throttling (or frequency change without corresponding voltage change), you're usually better off getting things done as soon as possible and then go into deep sleep instead. However, if you are about to emit smoke, you don't really have a whole lot of options.
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