On Mon, Dec 7, 2020 at 12:41 PM Hazem Mohamed Abuelfotoh <abuehaze@xxxxxxxxxx> wrote: > > Previously receiver buffer auto-tuning starts after receiving > one advertised window amount of data.After the initial > receiver buffer was raised by > commit a337531b942b ("tcp: up initial rmem to 128KB > and SYN rwin to around 64KB"),the receiver buffer may > take too long for TCP autotuning to start raising > the receiver buffer size. > commit 041a14d26715 ("tcp: start receiver buffer autotuning sooner") > tried to decrease the threshold at which TCP auto-tuning starts > but it's doesn't work well in some environments > where the receiver has large MTU (9001) especially with high RTT > connections as in these environments rcvq_space.space will be the same > as rcv_wnd so TCP autotuning will never start because > sender can't send more than rcv_wnd size in one round trip. > To address this issue this patch is decreasing the initial > rcvq_space.space so TCP autotuning kicks in whenever the sender is > able to send more than 5360 bytes in one round trip regardless the > receiver's configured MTU. > > Fixes: a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB") > Fixes: 041a14d26715 ("tcp: start receiver buffer autotuning sooner") > > Signed-off-by: Hazem Mohamed Abuelfotoh <abuehaze@xxxxxxxxxx> > --- > net/ipv4/tcp_input.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index 389d1b340248..f0ffac9e937b 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -504,13 +504,14 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb) > static void tcp_init_buffer_space(struct sock *sk) > { > int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win; > + struct inet_connection_sock *icsk = inet_csk(sk); > struct tcp_sock *tp = tcp_sk(sk); > int maxwin; > > if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) > tcp_sndbuf_expand(sk); > > - tp->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * tp->advmss); > + tp->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * icsk->icsk_ack.rcv_mss); I find using icsk->icsk_ack.rcv_mss misleading. I would either use TCP_MSS_DEFAULT , or maybe simply 0, since we had no samples yet, there is little point to use a magic value. Note that if a driver uses 16KB of memory to hold a 1500 bytes packet, then a 10 MSS GRO packet is consuming 160 KB of memory, which is bigger than tcp_rmem[1]. TCP could decide to drop these fat packets. I wonder if your patch does not work around a more fundamental issue, I am still unable to reproduce the issue.