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Commit cedb9bdc authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

vhost-net: skip head management if no outstanding 



For short packets zerocopy mode adds overhead
of managing heads which isn't necessary: we
could simly update used ring directly
same as with zerocopy disabled.

Things seem to run a bit faster if we detect
and bypass head management when zcopy isn't used.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 1280c27f

drivers/vhost/net.c

+7 −4
Original line number Original line Diff line number Diff line
@@ -241,7 +241,7 @@ static void handle_tx(struct vhost_net *net) 
	size_t hdr_size;

	size_t hdr_size;

	struct socket *sock;

	struct socket *sock;

	struct vhost_ubuf_ref *uninitialized_var(ubufs);

	struct vhost_ubuf_ref *uninitialized_var(ubufs);

	bool zcopy;

	bool zcopy, zcopy_used;





	/* TODO: check that we are running from vhost_worker? */

	/* TODO: check that we are running from vhost_worker? */

	sock = rcu_dereference_check(vq->private_data, 1);

	sock = rcu_dereference_check(vq->private_data, 1);
@@ -319,8 +319,11 @@ static void handle_tx(struct vhost_net *net) 
			       iov_length(vq->hdr, s), hdr_size);

			       iov_length(vq->hdr, s), hdr_size);

			break;

			break;

		}

		}

		zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN ||

				       vq->upend_idx != vq->done_idx);



		/* use msg_control to pass vhost zerocopy ubuf info to skb */

		/* use msg_control to pass vhost zerocopy ubuf info to skb */

		if (zcopy) {

		if (zcopy_used) {

			vq->heads[vq->upend_idx].id = head;

			vq->heads[vq->upend_idx].id = head;

			if (!vhost_net_tx_select_zcopy(net) ||

			if (!vhost_net_tx_select_zcopy(net) ||

			    len < VHOST_GOODCOPY_LEN) {

			    len < VHOST_GOODCOPY_LEN) {
@@ -348,7 +351,7 @@ static void handle_tx(struct vhost_net *net) 
		/* TODO: Check specific error and bomb out unless ENOBUFS? */

		/* TODO: Check specific error and bomb out unless ENOBUFS? */

		err = sock->ops->sendmsg(NULL, sock, &msg, len);

		err = sock->ops->sendmsg(NULL, sock, &msg, len);

		if (unlikely(err < 0)) {

		if (unlikely(err < 0)) {

			if (zcopy) {

			if (zcopy_used) {

				if (ubufs)

				if (ubufs)

					vhost_ubuf_put(ubufs);

					vhost_ubuf_put(ubufs);

				vq->upend_idx = ((unsigned)vq->upend_idx - 1) %

				vq->upend_idx = ((unsigned)vq->upend_idx - 1) %
@@ -362,7 +365,7 @@ static void handle_tx(struct vhost_net *net) 
		if (err != len)

		if (err != len)

			pr_debug("Truncated TX packet: "

			pr_debug("Truncated TX packet: "

				 " len %d != %zd\n", err, len);

				 " len %d != %zd\n", err, len);

		if (!zcopy)

		if (!zcopy_used)

			vhost_add_used_and_signal(&net->dev, vq, head, 0);

			vhost_add_used_and_signal(&net->dev, vq, head, 0);

		else

		else

			vhost_zerocopy_signal_used(net, vq);

			vhost_zerocopy_signal_used(net, vq);