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)
- 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?)
--
error compiling committee.c: too many arguments to function
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