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

[Jason Wang]

On 2018å05æ22æ 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