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Message-ID: <CAK6E8=eyy_i0UYywCar0idOkSFMSJd43HwAaW7YV+2nSS3B=UQ@mail.gmail.com>
Date: Thu, 27 Sep 2018 12:39:19 -0700
From: Yuchung Cheng <ycheng@...gle.com>
To: David Miller <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>
Cc: netdev <netdev@...r.kernel.org>,
Neal Cardwell <ncardwell@...gle.com>,
Wei Wang <weiwan@...gle.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] tcp: up initial rmem to 128KB and SYN rwin to
around 64KB
On Thu, Sep 27, 2018 at 11:21 AM, Yuchung Cheng <ycheng@...gle.com> wrote:
> 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.
Sorry please ignore this patch for now.
We need to adjust rbuf autotuning as well otherwise w/ larger init
rbuf it may increase too slowly during slow start. Will submit a v2
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Wei Wang <weiwan@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reviewed-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> ---
> 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 69c236943f56..dcf51fbf5ec7 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3896,8 +3896,8 @@ 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 d703a0b3b6a2..7a59f6a96212 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 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);
> 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) {
> @@ -257,11 +245,6 @@ 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);
> }
> --
> 2.19.0.605.g01d371f741-goog
>
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