tcp: enable MSG_ZEROCOPY
Enable support for MSG_ZEROCOPY to the TCP stack. TSO and GSO are
both supported. Only data sent to remote destinations is sent without
copying. Packets looped onto a local destination have their payload
copied to avoid unbounded latency.
Tested:
A 10x TCP_STREAM between two hosts showed a reduction in netserver
process cycles by up to 70%, depending on packet size. Systemwide,
savings are of course much less pronounced, at up to 20% best case.
msg_zerocopy.sh 4 tcp:
without zerocopy
tx=121792 (7600 MB) txc=0 zc=n
rx=60458 (7600 MB)
with zerocopy
tx=286257 (17863 MB) txc=286257 zc=y
rx=140022 (17863 MB)
This test opens a pair of sockets over veth, one one calls send with
64KB and optionally MSG_ZEROCOPY and on the other reads the initial
bytes. The receiver truncates, so this is strictly an upper bound on
what is achievable. It is more representative of sending data out of
a physical NIC (when payload is not touched, either).
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9dd6f4d..71b2556 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1165,6 +1165,7 @@ static int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
{
struct tcp_sock *tp = tcp_sk(sk);
+ struct ubuf_info *uarg = NULL;
struct sk_buff *skb;
struct sockcm_cookie sockc;
int flags, err, copied = 0;
@@ -1174,6 +1175,26 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
long timeo;
flags = msg->msg_flags;
+
+ if (flags & MSG_ZEROCOPY && size) {
+ if (sk->sk_state != TCP_ESTABLISHED) {
+ err = -EINVAL;
+ goto out_err;
+ }
+
+ skb = tcp_send_head(sk) ? tcp_write_queue_tail(sk) : NULL;
+ uarg = sock_zerocopy_realloc(sk, size, skb_zcopy(skb));
+ if (!uarg) {
+ err = -ENOBUFS;
+ goto out_err;
+ }
+
+ /* skb may be freed in main loop, keep extra ref on uarg */
+ sock_zerocopy_get(uarg);
+ if (!(sk_check_csum_caps(sk) && sk->sk_route_caps & NETIF_F_SG))
+ uarg->zerocopy = 0;
+ }
+
if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect)) {
err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size);
if (err == -EINPROGRESS && copied_syn > 0)
@@ -1297,7 +1318,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
err = skb_add_data_nocache(sk, skb, &msg->msg_iter, copy);
if (err)
goto do_fault;
- } else {
+ } else if (!uarg || !uarg->zerocopy) {
bool merge = true;
int i = skb_shinfo(skb)->nr_frags;
struct page_frag *pfrag = sk_page_frag(sk);
@@ -1335,6 +1356,13 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
page_ref_inc(pfrag->page);
}
pfrag->offset += copy;
+ } else {
+ err = skb_zerocopy_iter_stream(sk, skb, msg, copy, uarg);
+ if (err == -EMSGSIZE || err == -EEXIST)
+ goto new_segment;
+ if (err < 0)
+ goto do_error;
+ copy = err;
}
if (!copied)
@@ -1381,6 +1409,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
}
out_nopush:
+ sock_zerocopy_put(uarg);
return copied + copied_syn;
do_fault:
@@ -1397,6 +1426,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
if (copied + copied_syn)
goto out;
out_err:
+ sock_zerocopy_put_abort(uarg);
err = sk_stream_error(sk, flags, err);
/* make sure we wake any epoll edge trigger waiter */
if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 &&