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

Jason Wang
2018-05-21T09:08:17Z

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;
+ int head;
+ 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;
+
+ 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);
+ break;
+ }
+
+ len = init_iov_iter(vq, &msg.msg_iter, hdr_size, out);
+ if (len < 0)
+ break;
+
+ 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;
+ }
+
+ /* 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);
+ vhost_add_used_and_signal(&net->dev, vq, head, 0);
+ if (vhost_exceeds_weight(++sent_pkts, total_len)) {
+ vhost_poll_queue(&vq->poll);
+ break;
+ }
+ }
+out:
+ mutex_unlock(&vq->mutex);
+}
+
/* Expects to be always run from workqueue - which acts as
* read-size critical section for our kind of RCU. */
-static void handle_tx(struct vhost_net *net)
+static void handle_tx_zerocopy(struct vhost_net *net)
{
struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
struct vhost_virtqueue *vq = &nvq->vq;
@@ -512,7 +598,7 @@ static void handle_tx(struct vhost_net *net)
size_t hdr_size;
struct socket *sock;
struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
- bool zcopy, zcopy_used;
+ bool zcopy_used;
int sent_pkts = 0;

mutex_lock(&vq->mutex);
@@ -527,13 +613,10 @@ static void handle_tx(struct vhost_net *net)
vhost_net_disable_vq(net, vq);

hdr_size = nvq->vhost_hlen;
- zcopy = nvq->ubufs;

for (;;) {
/* Release DMAs done buffers first */
- if (zcopy)
- vhost_zerocopy_signal_used(net, vq);
-
+ vhost_zerocopy_signal_used(net, vq);

head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
ARRAY_SIZE(vq->iov),
@@ -559,9 +642,9 @@ static void handle_tx(struct vhost_net *net)
if (len < 0)
break;

- zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
- && !vhost_exceeds_maxpend(net)
- && vhost_net_tx_select_zcopy(net);
+ zcopy_used = len >= VHOST_GOODCOPY_LEN
+ && !vhost_exceeds_maxpend(net)
+ && vhost_net_tx_select_zcopy(net);

/* use msg_control to pass vhost zerocopy ubuf info to skb */
if (zcopy_used) {
@@ -620,6 +703,16 @@ static void handle_tx(struct vhost_net *net)
mutex_unlock(&vq->mutex);
}

+static void handle_tx(struct vhost_net *net)
+{
+ struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
+
+ if (nvq->ubufs)
+ handle_tx_zerocopy(net);
+ else
+ handle_tx_copy(net);
+}
+
static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
{
struct sk_buff *head;
--
2.7.4