virtio-net-pci does not enable ioeventfd for historical reasons (and
nobody ever checked whether it should be revisited). Note that other
backends do enable ioeventfd for virtio-net.
However, it has a major effect on performance. On Windows, throughput is
_multiplied_ by 2 or 3 on TCP_STREAM (on small packets it is "only" a 30%
improvement) and a little less so on TCP_MAERTS albeit still very much
statistically significant. Latency also has a single digit improvement.
This is not visible when using vhost, which forces ioeventfd=on, but it
is substantial without vhost. In addition, also on Windows and with the
RHEL 7.3 kernel, APICv seems to slow down virtio-net performance a bit,
but the penalty with this patch goes from -25% to -7%.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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