January 19, 201610 yr I've been monitoring my server having recently created my first windows VM for gaming and have noticed that even when the Windows VM is not doing anything, the server CPU use sits around 30% utilised. In the Windows VM, task manager shows 0-1% cpu use. Checking top, it seems to be the qemu-system-x86 eating the cpu. top - 15:06:11 up 4:22, 1 user, load average: 2.09, 0.94, 0.45 Tasks: 265 total, 1 running, 263 sleeping, 0 stopped, 1 zombie Cpu(s): 19.2%us, 2.9%sy, 0.0%ni, 64.1%id, 13.7%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 32977464k total, 31438000k used, 1539464k free, 183852k buffers Swap: 0k total, 0k used, 0k free, 20425076k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 7406 root 20 0 12.6g 8.3g 17m S 183 26.5 1:16.96 qemu-system-x86 3924 nobody 20 0 1242m 176m 19m S 1 0.5 5:12.01 mono This seems to mean that my cores never idle down (or keep bouncing up and down) and therefore idle power consumption is up quite a bit. Measured at the wall, my tower without the VM running uses 90watts, with the VM running and IDLE it is pulling 150 watts. Now I would accept the higher power use if the VM was actually being used, but as it is just sat idle it just seems like a waste of money! Does this also mean that 30% of the CPU isn't available for use to either the VM or unraid too, as qemu-system-x86 is using it? Would be good to understand if this is expected or not? Is anyone else seeing something similar?
January 19, 201610 yr Are you passing through a graphics card? That may account for some of the increase in power usage.. Although I'm not convinced that would explain the CPU use.
January 19, 201610 yr Author Are you passing through a graphics card? That may account for some of the increase in power usage.. Although I'm not convinced that would explain the CPU use. I am yes, although surely the graphics card is still drawing power at idle even when the VM isn't running?
January 19, 201610 yr I'm sure it is, but it's not rendering anything when the VM is off was my thinking...
January 20, 201610 yr Are you passing through a graphics card? That may account for some of the increase in power usage.. Although I'm not convinced that would explain the CPU use. I am yes, although surely the graphics card is still drawing power at idle even when the VM isn't running? When my GTX 780 is passed through to a running VM, the killawatt I have hooked up reports draw around 150watts. When I shut the VM down it drops to between 60-70 watts. So no, your idle GPU power draw is not the same with a VM running vs not.
January 20, 201610 yr Author OK thanks Jonp. Any comment on why the CPU use in the windows VM shows zero, but in top (or on the unraid dashboard) seems to hover at 30% use by the qemu-system-x86 process? Does this happen on your rig?
January 20, 201610 yr OK thanks Jonp. Any comment on why the CPU use in the windows VM shows zero, but in top (or on the unraid dashboard) seems to hover at 30% use by the qemu-system-x86 process? Does this happen on your rig? It can but everyone's config could be a little different. What you need to understand is that in addition to the CPU load generated by the VM itself, there is an number of threads generated for the emulator as well (for the virtual IO Controllers, etc).
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