vhost-net: check the support of mergeable buffer outside the receive loop

No need to check the support of mergeable buffer inside the recevie
loop as the whole handle_rx()_xx is in the read critical region.  So
this patch move it ahead of the receiving loop.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 59dad9fe52dd..9f57cd45fe8f 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -411,7 +411,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
                 .hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
         };
         size_t total_len = 0;
-        int err, headcount;
+        int err, headcount, mergeable;
         size_t vhost_hlen, sock_hlen;
         size_t vhost_len, sock_len;
         /* TODO: check that we are running from vhost_worker? */
@@ -427,6 +427,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
 
         vq_log = unlikely(vhost_has_feature(&net->dev, VHOST_F_LOG_ALL)) ?
                 vq->log : NULL;
+        mergeable = vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF);
 
         while ((sock_len = peek_head_len(sock->sk))) {
                 sock_len += sock_hlen;
@@ -476,7 +477,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
                         break;
                 }
                 /* TODO: Should check and handle checksum. */
-                if (vhost_has_feature(&net->dev, VIRTIO_NET_F_MRG_RXBUF) &&
+                if (likely(mergeable) &&
                     memcpy_toiovecend(vq->hdr, (unsigned char *)&headcount,
                                       offsetof(typeof(hdr), num_buffers),
                                       sizeof hdr.num_buffers)) {