does taking CPUs offline decrease idle power?

[jpsollie]

An idea I was playing with:
My server has 64 CPUs (threadripper 32 core). It is the central device at work.
During night, the device stays online, but off course, does almost nothing.
Would taking all but one CPUs (1-63) offline help improving idle power consumption?
off course, we all now we have powersave governors, but this is a different approach (I think).
Any ideas?
_________________
The power of Gentoo optimization (not overclocked): [img]https://www.passmark.com/baselines/V10/images/503714802842.png[/img]

[mike155]

Use a wattmeter and measure power consumption?

Alternatively, you could switch your cores to offline and monitor CPU temperature and CPU fan speed. If temperature and/or fan speed decrease, you'll know that offline mode consumes less power.

[molletts]

Your CPU will have a built-in power monitor which you could use to test this - the kernel driver for it is CONFIG_SENSORS_AMD_ENERGY, under Device Drivers -> Hardware Monitoring Support -> AMD RAPL MSR based Energy driver in menuconfig. I don't know how well it works as I don't have a Zen CPU to test it with.

I seem to remember that, when I played with offlining cores on my FX9590 to try and tame its idle temp a bit during a hot summer, the reading didn't really go down much even when I shut down all but one.

[eccerr0r]

depends on the cpu, but some cpus in sleep state is equivalent of unplugging already, so it couldn't go down much more anyway.
_________________
Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?