Merge branch 'TX-used-ring-batched-updating-for-vhost'

Jason Wang says:

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TX used ring batched updating for vhost

This series implement batch updating of used ring for TX. This help to
reduce the cache contention on used ring. The idea is first split
datacopy path from zerocopy, and do only batching for datacopy. This
is because zercopy had already supported its own batching.

TX PPS was increased 25.8% and Netperf TCP does not show obvious
differences.

The split of datapath will also be helpful for future implementation
like in order completion.
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Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>