Monday, August 10, 2009

(not) switching contexts.

a lot of bits have been spilled over virtual network performance in v-bus vs virtio-net/virtio-pci.. (aka alacrity vm vs traditional kvm/qemu).. this includes some pretty sensational(ist?) performance graphs: here.

There are lots of details (and details do matter) but the first-order issue can probably be summed up thusly, from Avi Kivity on lklm:

The current conjecture is that ioq outperforms virtio because the host side of ioq is implemented in the host kernel, while the host side of virtio is implemented in userspace.

Perhaps context switching isn't such a minor detail afterall.