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vhost-net: skip head management if no outstanding

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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>
This commit is contained in:
Michael S. Tsirkin 2012-12-06 17:00:18 +02:00
parent 1280c27f8e
commit cedb9bdce0
1 changed files with 7 additions and 4 deletions
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11
drivers/vhost/net.c
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@ -241,7 +241,7 @@ static void handle_tx(struct vhost_net *net)
size_t hdr_size; size_t hdr_size;
struct socket *sock; struct socket *sock;
struct vhost_ubuf_ref *uninitialized_var(ubufs); struct vhost_ubuf_ref *uninitialized_var(ubufs);
bool zcopy; bool zcopy, zcopy_used;
/* TODO: check that we are running from vhost_worker? */ /* TODO: check that we are running from vhost_worker? */
sock = rcu_dereference_check(vq->private_data, 1); sock = rcu_dereference_check(vq->private_data, 1);
@ -319,8 +319,11 @@ static void handle_tx(struct vhost_net *net)
iov_length(vq->hdr, s), hdr_size); iov_length(vq->hdr, s), hdr_size);
break; 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 */ /* use msg_control to pass vhost zerocopy ubuf info to skb */
if (zcopy) { if (zcopy_used) {
vq->heads[vq->upend_idx].id = head; vq->heads[vq->upend_idx].id = head;
if (!vhost_net_tx_select_zcopy(net) || if (!vhost_net_tx_select_zcopy(net) ||
len < VHOST_GOODCOPY_LEN) { len < VHOST_GOODCOPY_LEN) {
@ -348,7 +351,7 @@ static void handle_tx(struct vhost_net *net)
/* TODO: Check specific error and bomb out unless ENOBUFS? */ /* TODO: Check specific error and bomb out unless ENOBUFS? */
err = sock->ops->sendmsg(NULL, sock, &msg, len); err = sock->ops->sendmsg(NULL, sock, &msg, len);
if (unlikely(err < 0)) { if (unlikely(err < 0)) {
if (zcopy) { if (zcopy_used) {
if (ubufs) if (ubufs)
vhost_ubuf_put(ubufs); vhost_ubuf_put(ubufs);
vq->upend_idx = ((unsigned)vq->upend_idx - 1) % vq->upend_idx = ((unsigned)vq->upend_idx - 1) %
@ -362,7 +365,7 @@ static void handle_tx(struct vhost_net *net)
if (err != len) if (err != len)
pr_debug("Truncated TX packet: " pr_debug("Truncated TX packet: "
" len %d != %zd\n", err, len); " len %d != %zd\n", err, len);
if (!zcopy) if (!zcopy_used)
vhost_add_used_and_signal(&net->dev, vq, head, 0); vhost_add_used_and_signal(&net->dev, vq, head, 0);
else else
vhost_zerocopy_signal_used(net, vq); vhost_zerocopy_signal_used(net, vq);