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authorEric Dumazet <edumazet@google.com>2016-04-29 21:16:53 (GMT)
committerDavid S. Miller <davem@davemloft.net>2016-05-02 21:02:26 (GMT)
commitd41a69f1d390fa3f2546498103cdcd78b30676ff (patch)
tree6b277c34e05b64524f3863ef29d9c222ddf23579 /net/ipv4
parent5413d1babe8f10de13d72496c12b862eef8ba613 (diff)
downloadlinux-d41a69f1d390fa3f2546498103cdcd78b30676ff.tar.xz
tcp: make tcp_sendmsg() aware of socket backlog
Large sendmsg()/write() hold socket lock for the duration of the call, unless sk->sk_sndbuf limit is hit. This is bad because incoming packets are parked into socket backlog for a long time. Critical decisions like fast retransmit might be delayed. Receivers have to maintain a big out of order queue with additional cpu overhead, and also possible stalls in TX once windows are full. Bidirectional flows are particularly hurt since the backlog can become quite big if the copy from user space triggers IO (page faults) Some applications learnt to use sendmsg() (or sendmmsg()) with small chunks to avoid this issue. Kernel should know better, right ? Add a generic sk_flush_backlog() helper and use it right before a new skb is allocated. Typically we put 64KB of payload per skb (unless MSG_EOR is requested) and checking socket backlog every 64KB gives good results. As a matter of fact, tests with TSO/GSO disabled give very nice results, as we manage to keep a small write queue and smaller perceived rtt. Note that sk_flush_backlog() maintains socket ownership, so is not equivalent to a {release_sock(sk); lock_sock(sk);}, to ensure implicit atomicity rules that sendmsg() was giving to (possibly buggy) applications. In this simple implementation, I chose to not call tcp_release_cb(), but we might consider this later. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Alexei Starovoitov <ast@fb.com> Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/tcp.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4787f86..b945c2b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1136,11 +1136,12 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
/* This should be in poll */
sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
- mss_now = tcp_send_mss(sk, &size_goal, flags);
-
/* Ok commence sending. */
copied = 0;
+restart:
+ mss_now = tcp_send_mss(sk, &size_goal, flags);
+
err = -EPIPE;
if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
goto out_err;
@@ -1166,6 +1167,9 @@ new_segment:
if (!sk_stream_memory_free(sk))
goto wait_for_sndbuf;
+ if (sk_flush_backlog(sk))
+ goto restart;
+
skb = sk_stream_alloc_skb(sk,
select_size(sk, sg),
sk->sk_allocation,