Re: [RFC PATCH net-next 04/12] vhost_net: split out datacopy logic

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On 2018年05月22日 00:46, Jesse Brandeburg wrote:
On Mon, 21 May 2018 17:04:25 +0800 Jason wrote:
Instead of mixing zerocopy and datacopy logics, this patch tries to
split datacopy logic out. This results for a more compact code and
specific optimization could be done on top more easily.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
  drivers/vhost/net.c | 111 +++++++++++++++++++++++++++++++++++++++++++++++-----
  1 file changed, 102 insertions(+), 9 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 4ebac76..4682fcc 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -492,9 +492,95 @@ static bool vhost_has_more_pkts(struct vhost_net *net,
  	       likely(!vhost_exceeds_maxpend(net));
  }
+static void handle_tx_copy(struct vhost_net *net)
+{
+	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
+	struct vhost_virtqueue *vq = &nvq->vq;
+	unsigned out, in;
move "out" and "in" down to inside the for loop as well.

+	int head;
move this "head" declaration inside for-loop below.

Will do these in next version, basically this function were just copied from handle_tx_zerocopy and remove unnecessary parts. So I'm thinking an independent patch from the beginning to avoid changes in two places.

+	struct msghdr msg = {
+		.msg_name = NULL,
+		.msg_namelen = 0,
+		.msg_control = NULL,
+		.msg_controllen = 0,
+		.msg_flags = MSG_DONTWAIT,
+	};
+	size_t len, total_len = 0;
+	int err;
+	size_t hdr_size;
+	struct socket *sock;
+	struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
+	int sent_pkts = 0;
why do we need so many locals?

So it looks to me ubufs is unnecessary but all other is really needed.


+
+	mutex_lock(&vq->mutex);
+	sock = vq->private_data;
+	if (!sock)
+		goto out;
+
+	if (!vq_iotlb_prefetch(vq))
+		goto out;
+
+	vhost_disable_notify(&net->dev, vq);
+	vhost_net_disable_vq(net, vq);
+
+	hdr_size = nvq->vhost_hlen;
+
+	for (;;) {
+		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
+						ARRAY_SIZE(vq->iov),
+						&out, &in);
+		/* On error, stop handling until the next kick. */
+		if (unlikely(head < 0))
+			break;
+		/* Nothing new?  Wait for eventfd to tell us they refilled. */
+		if (head == vq->num) {
+			if (unlikely(vhost_enable_notify(&net->dev, vq))) {
+				vhost_disable_notify(&net->dev, vq);
+				continue;
+			}
+			break;
+		}
+		if (in) {
+			vq_err(vq, "Unexpected descriptor format for TX: "
+			       "out %d, int %d\n", out, in);
don't break strings, keep all the bits between " " together, even if it
is longer than 80 chars.

Ok.


+			break;
+		}
+
+		len = init_iov_iter(vq, &msg.msg_iter, hdr_size, out);
+		if (len < 0)
+			break;
same comment as previous patch, len is a size_t which is unsigned.

Yes.


+
+		total_len += len;
+		if (total_len < VHOST_NET_WEIGHT &&
+		    vhost_has_more_pkts(net, vq)) {
+			msg.msg_flags |= MSG_MORE;
+		} else {
+			msg.msg_flags &= ~MSG_MORE;
+		}
don't need { } here.

Right.

+
+		/* TODO: Check specific error and bomb out unless ENOBUFS? */
+		err = sock->ops->sendmsg(sock, &msg, len);
+		if (unlikely(err < 0)) {
+			vhost_discard_vq_desc(vq, 1);
+			vhost_net_enable_vq(net, vq);
+			break;
+		}
+		if (err != len)
+			pr_debug("Truncated TX packet: "
+				 " len %d != %zd\n", err, len);
single line " " string please


Will fix.

Thanks



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