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

Jesse Brandeburg
2018-05-21T16:46:52Z

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@redhat.com>
> ---
> 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.

> + 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?

> +
> + 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.

> + 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.

> +
> + 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.

> +
> + /* 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