On 04/21/11 02:07, Avi Kivity wrote: > On 04/21/2011 05:35 AM, Alex Williamson wrote: >> Device assignment via a VF provides the lowest latency and most >> bandwidth for *getting data off the host system*, though virtio/vhost is >> getting better. If all you care about is VM-VM on the same host or >> VM-host, then virtio is only limited by memory bandwidth/latency and >> host processor cycles. Your processor has 25GB/s of memory bandwidth. >> On the other hand, the VF has to send data all the way out to the wire >> and all the way back up through the NIC to get to the other VM/host. >> You're using a 1Gb/s NIC. Your results actually seem to indicate you're >> getting better than wire rate, so maybe you're only passing through an >> internal switch on the NIC, in any case, VFs are not optimal for >> communication within the same physical system. They are optimal for off >> host communication. Thanks, >> > > Note I think in both cases we can make significant improvements: > - for VFs, steer device interrupts to the cpus which run the vcpus that > will receive the interrupts eventually (ISTR some work about this, but > not sure) I don't understand your point here. I thought interrupts for the VF were only delivered to the guest, not the host. David > - for virtio, use a DMA engine to copy data (I think there exists code > in upstream which does this, but has this been enabled/tuned?) > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
