[PATCH 1/3] vhost-net: check the support of mergeable buffer outside the receive loop

[Jason Wang <jasowang@redhat.com>]

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>
---
 drivers/vhost/net.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 14fc189..95e49de 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -411,7 +411,7 @@ static void handle_rx_mergeable(struct vhost_net *net)
 	};
 
 	size_t total_len = 0;
-	int err, headcount;
+	int err, headcount, mergeable;
 	size_t vhost_hlen, sock_hlen;
 	size_t vhost_len, sock_len;
 	struct socket *sock = rcu_dereference(vq->private_data);
@@ -425,6 +425,7 @@ 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;
@@ -474,7 +475,7 @@ 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)) {