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SubjectRe: Changing CPU Speed while running Linux
On Wed, 13 Jun 2001, Magnus Sandberg wrote:

> I have a brand new Dell Inspiron 8000, laptop. It can run in 700 MHz or
> 850 MHz. The manual says that the machine/BIOS switches speed dependent on
> CPU load. I have not installed Linux yet, but it works with Win2000.

Intel Speedstep iirc. My Vaio also has it. My findings so far:

On mains it runs at 700MHz, whilst on batteries it drops to ~550MHz.
If I boot an ACPI enabled kernel, the speed changes according to CPU
load, but with a smaller window. I've seen it go as low as 50MHz,
but only up to a maximum of 200MHz. The fact that it only has a maximum
of 200MHz in this mode probably explains the need for the no-idle switch
in the current ACPI implementation.

As there are no public documents on Speedstep, it's not clear to me
whether this is a limitation of Speedstep, or the ACPI implementation.
Judging by the fact that Windows seems to run at full speed, I'd
be inclined to think the latter.



| Dave Jones.
| SuSE Labs

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