Not long ago, Steve, one of the founders of the ELRepo project, built new systems with the AMD II X4 Phenom processor. After hearing his positive comments, I replaced my old desktop with a new one equipped with a Phenom cpu.

Steve soon noticed that the machine consumed more power when it was running CentOS compared to when running Fedora. Turns out that, in CentOS, there is no per-core control — meaning when the system needs a higher processor power, all cores will shoot up to the maximum frequency. In Fedora, each core gets attenuated independently.

This issue was noted by a CentOS forum user, AlexAT, here. He not only reported it in the upstream bugzilla but came up with a fix later.

Using the patch provided by AlexAT, we built a kernel module kmod-powernow-k8 and released it through ELRepo. After installing kmod-powernow-k8, Steve saw that the system was now measured drawing ~110W at idle from the wall outlet, similar to the power consumption observed under Fedora 10 and under CentOS 4.7. So without kmod-powernow-k8 installed, the system was consuming ~40W (36%) more power at idle and the core temperature was running 8-10°C hotter than with kmod-powernow-k8 installed, making this a very environmentally friendly kmod.

So, if you have newer Opterons, the Phenoms or Phenoms II (or Kuma core Athlons X2), you should give this driver a try. Also, you would want a backported AMD K10 core temperature monitor driver module (kmod-k10temp) from ELRepo.

Let’s go green!