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: Michael S. Tsirkin <mst@redhat.com>
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 6a86deb..aa76ca7 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -241,7 +241,7 @@
size_t hdr_size;
struct socket *sock;
struct vhost_ubuf_ref *uninitialized_var(ubufs);
- bool zcopy;
+ bool zcopy, zcopy_used;
/* TODO: check that we are running from vhost_worker? */
sock = rcu_dereference_check(vq->private_data, 1);
@@ -319,8 +319,11 @@
iov_length(vq->hdr, s), hdr_size);
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 */
- if (zcopy) {
+ if (zcopy_used) {
vq->heads[vq->upend_idx].id = head;
if (!vhost_net_tx_select_zcopy(net) ||
len < VHOST_GOODCOPY_LEN) {
@@ -348,7 +351,7 @@
/* TODO: Check specific error and bomb out unless ENOBUFS? */
err = sock->ops->sendmsg(NULL, sock, &msg, len);
if (unlikely(err < 0)) {
- if (zcopy) {
+ if (zcopy_used) {
if (ubufs)
vhost_ubuf_put(ubufs);
vq->upend_idx = ((unsigned)vq->upend_idx - 1) %
@@ -362,7 +365,7 @@
if (err != len)
pr_debug("Truncated TX packet: "
" len %d != %zd\n", err, len);
- if (!zcopy)
+ if (!zcopy_used)
vhost_add_used_and_signal(&net->dev, vq, head, 0);
else
vhost_zerocopy_signal_used(net, vq);