CPU MSR register "tweak" module?

CPU MSR register "tweak" module?

[Nils Faerber]

Hello!
Recently I purchased an AMD E-450 based netbook - my first AMD CPU for a
long time. As expected Grub works perfectly on it - as does the Debian
Linux I did install.

Many AMD CPUs, and some Intel CPUs maybe too, can be tweaked for way
lower power consumption by modifying the CPU MSR registers to lower the
core voltage and eventually also the frequency (per P-state).

The drawback of this is that the new values are lost upon reboot or
suspend-to-disk. And additionally some of the Linux kernel drivers that
get loaded or re-initialised during boot/resume pick up those values
from those registers before user-space can re-setup them.

So I was wondering if there is a possibility to configure Grub in a way
that it will set-up specific registers with specific values. Ideally
using the Grub config file... a small table with register/value pairs
would be enough and they can just be written to the MSR registers
without additional magic, so such a function should be pretty easy to
implement - if it does not exist yet.

I did search through the docs and also had a brief look at the Grub
source but could not find something like that.

Cheers
  nils

-- 
kernel concepts GmbH       Tel: +49-271-771091-12
Sieghuetter Hauptweg 48
D-57072 Siegen             Mob: +49-176-21024535
http://www.kernelconcepts.de

Re: CPU MSR register "tweak" module?

[Vladimir 'φ-coder/phcoder' Serbinenko]

[-- Attachment #1: Type: text/plain, Size: 283 bytes --]


> I did search through the docs and also had a brief look at the Grub
> source but could not find something like that.


This isn't done as of now. But it's easy to code. I'd recommend plunging
forward and coding it.

-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 294 bytes --]

Re: CPU MSR register "tweak" module?

[Nils Faerber]

Am 28.09.2012 17:59, schrieb Vladimir 'φ-coder/phcoder' Serbinenko:
>> I did search through the docs and also had a brief look at the Grub
>> source but could not find something like that.
> 
> This isn't done as of now. But it's easy to code. I'd recommend plunging
> forward and coding it.

Oh boy - I feared a reply like that ;)

Since I have not done any Grub development yet, do you have some
keywords for me to get started? I.e. probably a very rough description
of how *you* would implement such a feature... it would help me to find
the right starting points.

Thanks!

Cheers
  nils

-- 
kernel concepts GmbH       Tel: +49-271-771091-12
Sieghuetter Hauptweg 48
D-57072 Siegen             Mob: +49-176-21024535
http://www.kernelconcepts.de