On Mon, 2011-04-25 at 13:49 -0600, David Ahern wrote: > > On 04/25/11 13:29, Alex Williamson wrote: > > So we're effectively getting host-host latency/throughput for the VF, > > it's just that in the 82576 implementation of SR-IOV, the VF takes a > > latency hit that puts it pretty close to virtio. Unfortunate. I think > > For host-to-VM using VFs is worse than virtio which is counterintuitive. > > > you'll find that passing the PF to the guests should be pretty close to > > that 185us latency. I would assume (hope) the higher end NICs reduce > > About that 185usec: do you know where the bottleneck is? It seems as if > the packet is held in some queue waiting for an event/timeout before it > is transmitted.
you might want to check the VF driver. I know versions of the ixgbevf driver have a throttled interrupt option which will increase latency with some settings. I don't remember if the igbvf driver has the same feature. If it does, you will want to turn this option off for best latency. > > David > > > > this, but it seems to be a hardware limitation, so it's hard to predict. > > Thanks, > > > > Alex -Andrew -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
