From 6ae705323b716ea7a8cc26bee79176398a9b2e89 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 1 Oct 2013 10:23:44 -0700 Subject: [PATCH] tcp: sndbuf autotuning improvements MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit tcp_fixup_sndbuf() is underestimating initial send buffer requirements. It was not noticed because big GSO packets were escaping the limitation, but with smaller TSO packets (or TSO/GSO/SG off), application hits sk_sndbuf before having a chance to fill enough packets in socket write queue. - initial cwnd can be bigger than 10 for specific routes - SKB_TRUESIZE() is a bit under real needs in some cases, because of power-of-two rounding in kmalloc() - Fast Recovery (RFC 5681 3.2) : Cubic needs 70% factor - Extra cushion (application might react slowly to POLLOUT) tcp_v4_conn_req_fastopen() needs to call tcp_init_metrics() before calling tcp_init_buffer_space() Then we realize tcp_new_space() should call tcp_fixup_sndbuf() instead of duplicating this stuff. Rename tcp_fixup_sndbuf() to tcp_sndbuf_expand() to be more descriptive. Signed-off-by: Eric Dumazet Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Acked-by: Maciej Żenczykowski Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 38 +++++++++++++++++++++++++------------- net/ipv4/tcp_ipv4.c | 2 +- 2 files changed, 26 insertions(+), 14 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 66aa816ad30b..cd65674ece92 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -267,11 +267,31 @@ static bool TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr * 1. Tuning sk->sk_sndbuf, when connection enters established state. */ -static void tcp_fixup_sndbuf(struct sock *sk) +static void tcp_sndbuf_expand(struct sock *sk) { - int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER); + const struct tcp_sock *tp = tcp_sk(sk); + int sndmem, per_mss; + u32 nr_segs; + + /* Worst case is non GSO/TSO : each frame consumes one skb + * and skb->head is kmalloced using power of two area of memory + */ + per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) + + MAX_TCP_HEADER + + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); + + per_mss = roundup_pow_of_two(per_mss) + + SKB_DATA_ALIGN(sizeof(struct sk_buff)); + + nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd); + nr_segs = max_t(u32, nr_segs, tp->reordering + 1); + + /* Fast Recovery (RFC 5681 3.2) : + * Cubic needs 1.7 factor, rounded to 2 to include + * extra cushion (application might react slowly to POLLOUT) + */ + sndmem = 2 * nr_segs * per_mss; - sndmem *= TCP_INIT_CWND; if (sk->sk_sndbuf < sndmem) sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); } @@ -376,7 +396,7 @@ void tcp_init_buffer_space(struct sock *sk) if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) tcp_fixup_rcvbuf(sk); if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) - tcp_fixup_sndbuf(sk); + tcp_sndbuf_expand(sk); tp->rcvq_space.space = tp->rcv_wnd; tp->rcvq_space.time = tcp_time_stamp; @@ -4723,15 +4743,7 @@ static void tcp_new_space(struct sock *sk) struct tcp_sock *tp = tcp_sk(sk); if (tcp_should_expand_sndbuf(sk)) { - int sndmem = SKB_TRUESIZE(max_t(u32, - tp->rx_opt.mss_clamp, - tp->mss_cache) + - MAX_TCP_HEADER); - int demanded = max_t(unsigned int, tp->snd_cwnd, - tp->reordering + 1); - sndmem *= 2 * demanded; - if (sndmem > sk->sk_sndbuf) - sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); + tcp_sndbuf_expand(sk); tp->snd_cwnd_stamp = tcp_time_stamp; } diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index b14266bb91eb..5d6b1a609da8 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1410,8 +1410,8 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk, inet_csk(child)->icsk_af_ops->rebuild_header(child); tcp_init_congestion_control(child); tcp_mtup_init(child); - tcp_init_buffer_space(child); tcp_init_metrics(child); + tcp_init_buffer_space(child); /* Queue the data carried in the SYN packet. We need to first * bump skb's refcnt because the caller will attempt to free it. -- 2.20.1