Re: [PATCH] virtio_net: introduce VIRTIO_NET_HDR_F_DATA_VALID

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Fri, 10 Jun 2011 14:28:28 +0300

On Fri, Jun 10, 2011 at 06:56:17PM +0800, Jason Wang wrote:

quoted

There's no need for the guest to validate the checksum if it have been
validated by host nics. So this patch introduces a new flag -
VIRTIO_NET_HDR_F_DATA_VALID which is used to bypass the checksum
examing in guest. The backend (tap/macvtap) may set this flag when
met skbs with CHECKSUM_UNNECESSARY to save cpu utilization.

No feature negotiation is needed as old driver just ignore this flag.

This wasn't required by the spec, but maybe it should be.

quoted

Iperf shows 12%-30% performance improvement for UDP traffic. For TCP,
when gro is on no difference as it produces skb with partial
checksum. But when gro is disabled, 20% or even higher improvement
could be measured by netperf.

Signed-off-by: Jason Wang <redacted>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Applied to net-next-2.6