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I have a 4X Xeon X7560 Dell r810 server that uses a lot of energy, even while idle (400 watts). I don't need all 4 CPUs active when the server is idle or under light load, so I wonder if I can save energy by disabling them.

I know you can dynamically disable logical cores ("processors" as Linux calls them) with echo 0 > /sys/devices/system/cpu/cpu[number]/online, but how can I disable an entire CPU socket while the system is running in a way that will prevent that CPU from consuming energy? And I also need to be able to re-enable them without rebooting. I tried disabling all lcores that were mapped to a socket, and I didn't see any change in idle power consumption.

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I doubt that disabling the cores in the Linux sysfs will save any power, unless the CPU supports such features like modern ARM CPUs do. The second issue you would have, shutting down one or more sockets, will be that each socket has a dedicated portion of RAM, which would also be unavailable if you shutdown that socket.

Best and maybe only way to save energy is to install and configure cpupower or any other tool that can downclock your CPU. Also check in the BIOS for such features.

  • Right, I was thinking the RAM might be a problem, and I was hoping there'd be some tool that would resolve that. The system is downclocking my CPUs to the minimum (about 50%) automatically, which is saving energy. – sudo Apr 16 '17 at 4:48

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