[PATCH 3/3] vhost_net: tx support batching

[Jason Wang]

This patch tries to utilize tuntap rx batching by peeking the tx
virtqueue during transmission, if there's more available buffers in
the virtqueue, set MSG_MORE flag for a hint for tuntap to batch the
packets. The maximum number of batched tx packets were specified
through a module parameter: tx_bached.

When use 16 as tx_batched:

Pktgen test shows 16% on tx pps in guest.
Netperf test does not show obvious regression.

For safety, 1 were used as the default value for tx_batched.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/vhost/net.c   | 15 ++++++++++++++-
 drivers/vhost/vhost.c |  1 +
 drivers/vhost/vhost.h |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 5dc128a..51c378e 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -35,6 +35,10 @@ module_param(experimental_zcopytx, int, 0444);
 MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
 		                       " 1 -Enable; 0 - Disable");
 
+static int tx_batched = 1;
+module_param(tx_batched, int, 0444);
+MODULE_PARM_DESC(tx_batched, "Number of patches batched in TX");
+
 /* Max number of bytes transferred before requeueing the job.
  * Using this limit prevents one virtqueue from starving others. */
 #define VHOST_NET_WEIGHT 0x80000
@@ -454,6 +458,16 @@ static void handle_tx(struct vhost_net *net)
 			msg.msg_control = NULL;
 			ubufs = NULL;
 		}
+		total_len += len;
+		if (vq->delayed < tx_batched &&
+		    total_len < VHOST_NET_WEIGHT &&
+		    !vhost_vq_avail_empty(&net->dev, vq)) {
+			vq->delayed++;
+			msg.msg_flags |= MSG_MORE;
+		} else {
+			vq->delayed = 0;
+			msg.msg_flags &= ~MSG_MORE;
+		}
 		/* TODO: Check specific error and bomb out unless ENOBUFS? */
 		err = sock->ops->sendmsg(sock, &msg, len);
 		if (unlikely(err < 0)) {
@@ -472,7 +486,6 @@ static void handle_tx(struct vhost_net *net)
 			vhost_add_used_and_signal(&net->dev, vq, head, 0);
 		else
 			vhost_zerocopy_signal_used(net, vq);
-		total_len += len;
 		vhost_net_tx_packet(net);
 		if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
 			vhost_poll_queue(&vq->poll);
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index fdf4cdf..bc362c7 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -311,6 +311,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	vq->busyloop_timeout = 0;
 	vq->umem = NULL;
 	vq->iotlb = NULL;
+	vq->delayed = 0;
 }
 
 static int vhost_worker(void *data)
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 78f3c5f..9f81a94 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -141,6 +141,7 @@ struct vhost_virtqueue {
 	bool user_be;
 #endif
 	u32 busyloop_timeout;
+	int delayed;
 };
 
 struct vhost_msg_node {
-- 
2.7.4