Following on my last playing around with Intel power stats, I tried Powertop to further reduce my lightly loaded server’s power usage. Powertop watches the kernel to see when interrupts wake the system from idle, then gives you hints on how to turn those power drains off. I turned on a bunch of their power saving tips to see what would happen. Honestly, not much, < 5 watts or 10% of my server’s power usage. And some of what I did was pretty aggressive, like disabling system backups and databases and email that I can’t do for real. Other things were more benign, tuning various parameters (like a 15 second disk flush instead of 5 second) but given how little benefit it has I’m not making changes permanent.
The changes I made are easiest to see in the INdividual interrupts graph, around Sun 16:00. You can see we go from 150 interrupts / second to about 50. Fewer interrupts = more idle time. It’s also sort of visible in the CPU scaling graph. But it’s not meaningfully visible in the UPS power graph.
There’s a bigger change in these graphs, around Sat 20:00. That’s when I shut down mongodb. Mongo seems to constantly be doing something even when sitting idle. I wasn’t seeing the 15% CPU some users report, but it’s a lot more than zero. Still has no meaningful impact on power consumption so it’s probably not relevant.