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tcp: up initial rmem to 128KB and SYN rwin to around 64KB

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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>
This commit is contained in:
Yuchung Cheng
2018-09-27 11:21:19 -07:00
committed by David S. Miller
parent 3ff6cde846
commit a337531b94
3 changed files with 8 additions and 46 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
net/ipv4/tcp_input.c
View File

@@ -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);