Idle SL/Centos machine in KVM leads to 5 Watt more power usage

December 25, 2011

My home server needs in idle state less than 25 Watt (Intel Core i3-2100, SSD for the system, 2TB HD) but as soon as a KVM machine runs I need 30 Watt. It does not matter if the virtual machine is idle. As guest I’ve a RHEL6 Clone (Scientific Linux) running with the virtualization modules loaded:


# lsmod | grep virt
virtio_balloon 4281 0
virtio_net 15741 0
virtio_blk 5692 3
virtio_pci 6653 0
virtio_ring 7169 4 virtio_balloon,virtio_net,virtio_blk,virtio_pci
virtio 4824 4 virtio_balloon,virtio_net,virtio_blk,virtio_pci

But take a look at the screenshots – the first without running KVM virtual machine …

… and as you see the CPU is 98% of the time in C3 (lowest power consumption). And flowing screenshot shows the same computer after starting a KVM virtual maschine and waiting some minutes to settle ….

… and now we’re 20% in C1 and only 75% in C3, and the reason with the highest percentage is qemu-kvm.

Now you ask how I know the power usage increase by 5 Watt? I have have a Watt-meter connected between the power outlet and the computer to measure the power usage.

Anyway, I currently don’t have a solution for this, maybe a reader has.

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