Commit 8b949bef authored Sep 05, 2017 by Jason Wang Committed by David S. Miller Sep 05, 2017

vhost_net: correctly check tx avail during rx busy polling



We check tx avail through vhost_enable_notify() in the past which is
wrong since it only checks whether or not guest has filled more
available buffer since last avail idx synchronization which was just
done by vhost_vq_avail_empty() before. What we really want is checking
pending buffers in the avail ring. Fix this by calling
vhost_vq_avail_empty() instead.

This issue could be noticed by doing netperf TCP_RR benchmark as
client from guest (but not host). With this fix, TCP_RR from guest to
localhost restores from 1375.91 trans per sec to 55235.28 trans per
sec on my laptop (Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz).

Fixes: 03088137 ("vhost_net: basic polling support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5482a978

drivers/vhost/net.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -635,8 +635,13 @@ static int vhost_net_rx_peek_head_len(struct vhost_net net, struct sock sk)

		preempt_enable();

		if (vhost_enable_notify(&net->dev, vq))
		if (!vhost_vq_avail_empty(&net->dev, vq))
		vhost_poll_queue(&vq->poll);
		else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
		vhost_disable_notify(&net->dev, vq);
		vhost_poll_queue(&vq->poll);
		}

		mutex_unlock(&vq->mutex);

		len = peek_head_len(rvq, sk);

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