Centrino: undervolting and further reducing heat

[Daniel Bonniot <Daniel.Bonniot@inria.fr>]

Hi,

I have a dothan 1.6 GHz processor, and i've been investigating how to reduce 
heat to minimize fan usage. One very promising avenue is undervolting. 
According to several online articles, there is a large potential for 
undervolting. I ended up modifying speedstep-centrino.c to test it out. 
Results are very positive: it can run under heavy load at 1.6Ghz with only 
972mV (down from 1340mV). This decreased temperature by 10°C! At 600MHz, the 
minimum 700mV was sufficient.

I understand that the driver needs to be conservative by default, but given 
the huge benefits, it would make a lot of sense to offer a way to specify 
lower voltages to those who want to. Has anybody investigated this 
possibility, or already started working on it? What would be a good interface 
to specify the voltages?


Independently of this feature, I wonder how it's possible to further reduce 
consumption when the system is mostly ideal, and even 600MHz is more than 
needed. The idea being to let the system cool down even more in that case. Is 
there any existing way to achive this on linux? One possibility I found in the 
intel docs is the IA32_THERM_CONTROL MSR, which can reduce clock speed by 
12.5% to 87.5%. Am I right in thinking that it could be combined with 
speedstep to achieve even lower power consumption states? Are there other 
possibilities?

Cheers,

Daniel