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vhost_net: correctly check tx avail during rx busy polling

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[ Upstream commit 8b949bef9172ca69d918e93509a4ecb03d0355e0 ]

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: 030881372460 ("vhost_net: basic polling support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jason Wang 2017-09-05 09:22:05 +08:00 committed by Greg Kroah-Hartman
parent 90406e68e4
commit f5755c0e87
1 changed files with 6 additions and 1 deletions
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7
drivers/vhost/net.c
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@ -537,8 +537,13 @@ 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(sk);