I have a Proxmox server running two Opteron 6272 CPUs on an Asus KGPE-D16 (chosen because it was the fastest computer that supported Libreboot, although I haven’t gotten around to installing it). Using normal BIOS settings, it’s drawing just under 100W at idle, measured via smart plug reported in Home Assistant. With aggressive efficiency settings (PowerCap to P-state 4 and disabling CPU 2 entirely) it idles at 70W. It’s a server, not a gaming PC, so it doesn’t appear to have any options for underclocking or adjusting voltage.
Anybody know of any other ways (maybe software-based) to get the power draw down further?
If you’ve optimized your BIOS settings (balanced mode or power saving wherever possible), the only other option is removing extraneous hardware. All hardware power use (disks, HBAs, other adapters and controllers) adds up. I managed to get idle power consumption of an HP DL-380 G9 down to about 60w (started at 210w) by removing the disks, RAID controller and battery, fiber channel adapters, and extra Ethernet adapter. Each SAS disk I removed saved me 10w. I used one M.2 drive in a PCI adapter instead.
Like you mentioned, these aren’t designed to save power. That Opteron (and the chip set) hales from a time before “performance per watt” was a thing.