[RFC v2 3/7] vsock: batch buffers in tx

[Guo Zhi <qtxuning1999@sjtu.edu.cn>]

Vsock uses buffers in order, and for tx driver doesn't have to
know the length of the buffer. So we can do a batch for vsock if
in order negotiated, only write one used ring for a batch of buffers

Signed-off-by: Guo Zhi <qtxuning1999@sjtu.edu.cn>
---
 drivers/vhost/vsock.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 368330417bde..b0108009c39a 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -500,6 +500,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
 	int head, pkts = 0, total_len = 0;
 	unsigned int out, in;
 	bool added = false;
+	int last_head = -1;
 
 	mutex_lock(&vq->mutex);
 
@@ -551,10 +552,16 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
 		else
 			virtio_transport_free_pkt(pkt);
 
-		vhost_add_used(vq, head, 0);
+		if (!vhost_has_feature(vq, VIRTIO_F_IN_ORDER))
+			vhost_add_used(vq, head, 0);
+		else
+			last_head = head;
 		added = true;
 	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
 
+	/* If in order feature negotiaged, we can do a batch to increase performance */
+	if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER) && last_head != -1)
+		vhost_add_used(vq, last_head, 0);
 no_more_replies:
 	if (added)
 		vhost_signal(&vsock->dev, vq);
-- 
2.17.1