Power Saving with the Athlon MP

My server uses a pair of older Athlon MP chips which do not support PowerNow. Since this computer runs 24/7, I suspect it’s responsible for a substantial chunk of my monthly power bill. Today I discovered a way to reduce the power consumption.

First, I used my trusty Kill-A-Watt to get a baseline measurement. The server draws roughly 207 W at idle:

Before: 207 Watts

Now for the fun part. I applied this ACPI kernel patch to my kernel and built the amd76x_pm module. This patch enables the ACPI C2 and C3 processor states, which for some reason are otherwise disabled.

A quick reboot and modprobe later, I was greeted with this:

After: 113 Watts

There are a handful of warnings on the net about crashes, etc., when using the amd76x_pm code. So far, so good for me — But I’ll update this post if I experience any instability.

Update, Sunday 4:30 PM: Kernel Panic. Doh! Reboot and cross fingers…

Update, Monday 6:30 AM: Another crash. Although I didn’t mention this previously, I also enabled CONFIG_HIGH_RES_TIMERS and CONFIG_NO_HZ (Dynamic Ticks) in my new kernel. Maybe one of those is the cuplrit. I’m going to do the easiest thing, and pull amd76x_pm.ko for a while. We’ll see how it goes.

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