path: root/net/ipv4/tcp_output.c
diff options
authorYuchung Cheng <ycheng@google.com>2018-09-27 11:21:19 -0700
committerDavid S. Miller <davem@davemloft.net>2018-09-29 11:22:22 -0700
commita337531b942bd8a03e7052444d7e36972aac2d92 (patch)
tree32b97fbbf43d08936e0fbe9227158b0ea6508d36 /net/ipv4/tcp_output.c
parenthns3: Another build fix. (diff)
tcp: up initial rmem to 128KB and SYN rwin to around 64KB
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>
Diffstat (limited to 'net/ipv4/tcp_output.c')
1 files changed, 4 insertions, 21 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index fe7855b090e4..059b67af28b1 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -195,21 +195,6 @@ 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.
@@ -244,7 +229,10 @@ 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);
- (*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) {
@@ -257,11 +245,6 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
- 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);