tcp: splice as many packets as possible at once (33966dd0) · Commits · 戴 / test

As spotted by Willy Tarreau, current splice() from tcp socket to pipe is not optimal. It processes at most one segment per call. This results in low performance and very high overhead due to syscall rate when splicing from interfaces which do not support LRO. Willy provided a patch inside tcp_splice_read(), but a better fix is to let tcp_read_sock() process as many segments as possible, so that tcp_rcv_space_adjust() and tcp_cleanup_rbuf() are called less often. With this change, splice() behaves like tcp_recvmsg(), being able to consume many skbs in one system call. With typical 1460 bytes of payload per frame, that means splice(SPLICE_F_NONBLOCK) can return 16*1460 = 23360 bytes. Signed-off-by:

Willy Tarreau <w@1wt.eu> Signed-off-by:

Eric Dumazet <dada1@cosmosbay.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -522,8 +522,12 @@ static int tcp_splice_data_recv(read_descriptor_t rd_desc, struct sk_buff skb,
		unsigned int offset, size_t len)
		{
		struct tcp_splice_state *tss = rd_desc->arg.data;
		int ret;

		return skb_splice_bits(skb, offset, tss->pipe, tss->len, tss->flags);
		ret = skb_splice_bits(skb, offset, tss->pipe, rd_desc->count, tss->flags);
		if (ret > 0)
		rd_desc->count -= ret;
		return ret;
		}

		static int __tcp_splice_read(struct sock sk, struct tcp_splice_state tss)
		@@ -531,6 +535,7 @@ static int __tcp_splice_read(struct sock sk, struct tcp_splice_state tss)
		/* Store TCP splice context information in read_descriptor_t. */
		read_descriptor_t rd_desc = {
		.arg.data = tss,
		.count = tss->len,
		};

		return tcp_read_sock(sk, &rd_desc, tcp_splice_data_recv);
		@@ -611,11 +616,13 @@ ssize_t tcp_splice_read(struct socket sock, loff_t ppos,
		tss.len -= ret;
		spliced += ret;

		if (!timeo)
		break;
		release_sock(sk);
		lock_sock(sk);

		if (sk->sk_err \|\| sk->sk_state == TCP_CLOSE \|\|
		(sk->sk_shutdown & RCV_SHUTDOWN) \|\| !timeo \|\|
		(sk->sk_shutdown & RCV_SHUTDOWN) \|\|
		signal_pending(current))
		break;
		}

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