From: Yuchung Cheng ycheng@google.com
[ Upstream commit a337531b942bd8a03e7052444d7e36972aac2d92 ]
Previously TCP initial receive buffer is ~87KB by default and the initial receive window is ~29KB (20 MSS). This patch changes the two numbers to 128KB and ~64KB (rounding down to the multiples of MSS) respectively. The patch also simplifies the calculations s.t. the two numbers are directly controlled by sysctl tcp_rmem[1]:
1) Initial receiver buffer budget (sk_rcvbuf): while this should be configured via sysctl tcp_rmem[1], previously tcp_fixup_rcvbuf() always override and set a larger size when a new connection establishes.
2) Initial receive window in SYN: previously it is set to 20 packets if MSS <= 1460. The number 20 was based on the initial congestion window of 10: the receiver needs twice amount to avoid being limited by the receive window upon out-of-order delivery in the first window burst. But since this only applies if the receiving MSS <= 1460, connection using large MTU (e.g. to utilize receiver zero-copy) may be limited by the receive window.
With this patch TCP memory configuration is more straight-forward and more properly sized to modern high-speed networks by default. Several popular stacks have been announcing 64KB rwin in SYNs as well.
Signed-off-by: Yuchung Cheng ycheng@google.com Signed-off-by: Wei Wang weiwan@google.com Signed-off-by: Neal Cardwell ncardwell@google.com Signed-off-by: Eric Dumazet edumazet@google.com Reviewed-by: Soheil Hassas Yeganeh soheil@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp.c | 4 ++-- net/ipv4/tcp_input.c | 25 ++----------------------- net/ipv4/tcp_output.c | 25 ++++--------------------- 3 files changed, 8 insertions(+), 46 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 647ba447bf1ab..a7a804bece7ac 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3910,8 +3910,8 @@ void __init tcp_init(void) init_net.ipv4.sysctl_tcp_wmem[2] = max(64*1024, max_wshare);
init_net.ipv4.sysctl_tcp_rmem[0] = SK_MEM_QUANTUM; - init_net.ipv4.sysctl_tcp_rmem[1] = 87380; - init_net.ipv4.sysctl_tcp_rmem[2] = max(87380, max_rshare); + init_net.ipv4.sysctl_tcp_rmem[1] = 131072; + init_net.ipv4.sysctl_tcp_rmem[2] = max(131072, max_rshare);
pr_info("Hash tables configured (established %u bind %u)\n", tcp_hashinfo.ehash_mask + 1, tcp_hashinfo.bhash_size); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 14a6a489937c1..0e2b07be08585 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -426,26 +426,7 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb) } }
-/* 3. Tuning rcvbuf, when connection enters established state. */ -static void tcp_fixup_rcvbuf(struct sock *sk) -{ - u32 mss = tcp_sk(sk)->advmss; - int rcvmem; - - rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) * - tcp_default_init_rwnd(mss); - - /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency - * Allow enough cushion so that sender is not limited by our window - */ - if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) - rcvmem <<= 2; - - if (sk->sk_rcvbuf < rcvmem) - sk->sk_rcvbuf = min(rcvmem, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]); -} - -/* 4. Try to fixup all. It is made immediately after connection enters +/* 3. Try to fixup all. It is made immediately after connection enters * established state. */ void tcp_init_buffer_space(struct sock *sk) @@ -454,8 +435,6 @@ void tcp_init_buffer_space(struct sock *sk) struct tcp_sock *tp = tcp_sk(sk); int maxwin;
- if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) - tcp_fixup_rcvbuf(sk); if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) tcp_sndbuf_expand(sk);
@@ -485,7 +464,7 @@ void tcp_init_buffer_space(struct sock *sk) tp->snd_cwnd_stamp = tcp_jiffies32; }
-/* 5. Recalculate window clamp after socket hit its memory bounds. */ +/* 4. Recalculate window clamp after socket hit its memory bounds. */ static void tcp_clamp_window(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 2697e4397e46c..53f910bb55087 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -179,21 +179,6 @@ static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts, inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); }
- -u32 tcp_default_init_rwnd(u32 mss) -{ - /* Initial receive window should be twice of TCP_INIT_CWND to - * enable proper sending of new unsent data during fast recovery - * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a - * limit when mss is larger than 1460. - */ - u32 init_rwnd = TCP_INIT_CWND * 2; - - if (mss > 1460) - init_rwnd = max((1460 * init_rwnd) / mss, 2U); - return init_rwnd; -} - /* Determine a window scaling and initial window to offer. * Based on the assumption that the given amount of space * will be offered. Store the results in the tp structure. @@ -228,7 +213,10 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss, if (sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows) (*rcv_wnd) = min(space, MAX_TCP_WINDOW); else - (*rcv_wnd) = space; + (*rcv_wnd) = min_t(u32, space, U16_MAX); + + if (init_rcv_wnd) + *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
(*rcv_wscale) = 0; if (wscale_ok) { @@ -241,11 +229,6 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss, (*rcv_wscale)++; } } - - if (!init_rcv_wnd) /* Use default unless specified otherwise */ - init_rcv_wnd = tcp_default_init_rwnd(mss); - *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss); - /* Set the clamp no higher than max representable value */ (*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp); }