[ltp] does anybody know how to calculate cpu voltage for each MHz?

[Niko Ehrenfeuchter]

Hi,

On Thu, 2004-07-29 at 19:39, Jenix wrote:
> hi.
> 
> i just realized my X40 Pentium-M 723 CPU uses less voltage then X31
> Pentium-M CPU.
> 
> For example, regarding to Intel Documents, 
> 
> when eariler M 1.0GHz CPU gets 600MHz clock, it uses 0.844 voltage,
> 
> but, when X40 1.00GHz CPU ( pentium-m 723 ) gets 600MHz clock,
> 
> it uses 0.812 voltage.
> 
> BUT, the centrino cpu freq source code in kernel does not have
> information about that, and it cannot also support less CPU clock. (
> when i use windows, i can set Slowest CPU and i get a 219MHz clock. )

iirc, you don't have to care about setting the voltage of the cpu, since
this is achieved by switching the frequency. The chipset not only
changes the frequency but also adjusts the voltage. So this is not a
software-issue, but it depends on the specific model and revision of
your cpu-chipset combination.

Windows displays pseudo-speeds, since there are no additional
frequencies for speedstepping (speedstep-centrino supports them all).
The 'lower' speed of the cpu in windows is achieved via ACPI throttling,
which is completeley independent from speedstepping - and can be done
simultaneously.

Since I haven't found a daemon that supports ACPI-throttling, I have
started to write a patch for the cpudyn[1] cpufreq-daemon (i chose this
one as a starting point since it already contains some functionality for
throttling, though as an _alternative_ to freqency-scaling).

While it already works, I'm not satisfied with the results yet since it
badly influences the responsiveness of the system - work's in progress
:)

Hope that helps.

Regards,
Niko

--

[1] http://mnm.uib.es/~gallir/cpudyn/