Re: PPro power consumption while executing "hlt"

Kimon Berlin (
Tue, 8 Apr 1997 18:17:58 +0100

> does anyone know why the PPro doesn't use less power when running idle
> and using "hlt" instruction then when running e.g. a idle loop in user
> space using
> main() { while (1) ; }
> I just got a power meter and with 486 and 586 CPUs there is a significant
> difference between idle Linux system and running any user process.
> with a PPro this is max 1W difference; I have to do memory access etc.
> to use +5-6W rel. to idle mode.
> does anyone know details about the halt/idle stuff for P5/P6 CPUs ?

This is controlled by the "low power enable" bit in EBL_CR_POWERON
(MSR 0x2a, bit 26). Your configuration probably has this set to 0.


Kimon Berlin - Hewlett-Packard Performance Desktop Computing Operation R&D
"Linux is growing at unbelievable speed in the scientific market."
[Rene Brun, CERN]