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Date: Tue, 5 Feb 2013 09:47:59 -0800
From: Yuchung Cheng <ycheng@...gle.com>
To: Stephen Hemminger <stephen@...workplumber.org>
Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: remove Appropriate Byte Count support
On Tue, Feb 5, 2013 at 9:25 AM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> TCP Appropriate Byte Count was added by me, but later disabled.
> There is no point in maintaining it since it is a potential source
> of bugs and Linux already implements other better window protection
> heuristics.
+1
>
> Signed-off-by: Stephen Hemminger <stephen@...workplumber.org>
>
> --- a/Documentation/networking/ip-sysctl.txt 2013-02-05 09:22:44.379791669 -0800
> +++ b/Documentation/networking/ip-sysctl.txt 2013-02-05 09:23:13.035421064 -0800
> @@ -130,17 +130,6 @@ somaxconn - INTEGER
> Defaults to 128. See also tcp_max_syn_backlog for additional tuning
> for TCP sockets.
>
> -tcp_abc - INTEGER
> - Controls Appropriate Byte Count (ABC) defined in RFC3465.
> - ABC is a way of increasing congestion window (cwnd) more slowly
> - in response to partial acknowledgments.
> - Possible values are:
> - 0 increase cwnd once per acknowledgment (no ABC)
> - 1 increase cwnd once per acknowledgment of full sized segment
> - 2 allow increase cwnd by two if acknowledgment is
> - of two segments to compensate for delayed acknowledgments.
> - Default: 0 (off)
> -
> tcp_abort_on_overflow - BOOLEAN
> If listening service is too slow to accept new connections,
> reset them. Default state is FALSE. It means that if overflow
> --- a/include/net/tcp.h 2013-02-05 09:22:44.379791669 -0800
> +++ b/include/net/tcp.h 2013-02-05 09:23:13.035421064 -0800
> @@ -279,7 +279,6 @@ extern int sysctl_tcp_dma_copybreak;
> extern int sysctl_tcp_nometrics_save;
> extern int sysctl_tcp_moderate_rcvbuf;
> extern int sysctl_tcp_tso_win_divisor;
> -extern int sysctl_tcp_abc;
> extern int sysctl_tcp_mtu_probing;
> extern int sysctl_tcp_base_mss;
> extern int sysctl_tcp_workaround_signed_windows;
> --- a/kernel/sysctl_binary.c 2013-02-05 09:22:44.379791669 -0800
> +++ b/kernel/sysctl_binary.c 2013-02-05 09:23:13.035421064 -0800
> @@ -387,7 +387,6 @@ static const struct bin_table bin_net_ip
> { CTL_INT, NET_TCP_MODERATE_RCVBUF, "tcp_moderate_rcvbuf" },
> { CTL_INT, NET_TCP_TSO_WIN_DIVISOR, "tcp_tso_win_divisor" },
> { CTL_STR, NET_TCP_CONG_CONTROL, "tcp_congestion_control" },
> - { CTL_INT, NET_TCP_ABC, "tcp_abc" },
> { CTL_INT, NET_TCP_MTU_PROBING, "tcp_mtu_probing" },
> { CTL_INT, NET_TCP_BASE_MSS, "tcp_base_mss" },
> { CTL_INT, NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS, "tcp_workaround_signed_windows" },
> --- a/net/ipv4/sysctl_net_ipv4.c 2013-02-05 09:22:49.035731453 -0800
> +++ b/net/ipv4/sysctl_net_ipv4.c 2013-02-05 09:23:13.035421064 -0800
> @@ -633,13 +633,6 @@ static struct ctl_table ipv4_table[] = {
> .proc_handler = proc_tcp_congestion_control,
> },
> {
> - .procname = "tcp_abc",
> - .data = &sysctl_tcp_abc,
> - .maxlen = sizeof(int),
> - .mode = 0644,
> - .proc_handler = proc_dointvec,
> - },
> - {
> .procname = "tcp_mtu_probing",
> .data = &sysctl_tcp_mtu_probing,
> .maxlen = sizeof(int),
> --- a/net/ipv4/tcp_cong.c 2013-02-05 09:22:44.379791669 -0800
> +++ b/net/ipv4/tcp_cong.c 2013-02-05 09:23:13.035421064 -0800
> @@ -311,26 +311,10 @@ void tcp_slow_start(struct tcp_sock *tp)
> int cnt; /* increase in packets */
> unsigned int delta = 0;
>
> - /* RFC3465: ABC Slow start
> - * Increase only after a full MSS of bytes is acked
> - *
> - * TCP sender SHOULD increase cwnd by the number of
> - * previously unacknowledged bytes ACKed by each incoming
> - * acknowledgment, provided the increase is not more than L
> - */
> - if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
> - return;
> -
> if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
> cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
> else
> cnt = tp->snd_cwnd; /* exponential increase */
> -
> - /* RFC3465: ABC
> - * We MAY increase by 2 if discovered delayed ack
> - */
> - if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
> - cnt <<= 1;
> tp->bytes_acked = 0;
Is bytes_acked still needed?
>
> tp->snd_cwnd_cnt += cnt;
> @@ -372,20 +356,9 @@ void tcp_reno_cong_avoid(struct sock *sk
> /* In "safe" area, increase. */
> if (tp->snd_cwnd <= tp->snd_ssthresh)
> tcp_slow_start(tp);
> -
> /* In dangerous area, increase slowly. */
> - else if (sysctl_tcp_abc) {
> - /* RFC3465: Appropriate Byte Count
> - * increase once for each full cwnd acked
> - */
> - if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
> - tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
> - if (tp->snd_cwnd < tp->snd_cwnd_clamp)
> - tp->snd_cwnd++;
> - }
> - } else {
> + else
> tcp_cong_avoid_ai(tp, tp->snd_cwnd);
> - }
> }
> EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
>
> --- a/net/ipv4/tcp_input.c 2013-02-05 09:22:49.035731453 -0800
> +++ b/net/ipv4/tcp_input.c 2013-02-05 09:23:13.039421013 -0800
> @@ -98,7 +98,6 @@ int sysctl_tcp_frto_response __read_most
> int sysctl_tcp_thin_dupack __read_mostly;
>
> int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
> -int sysctl_tcp_abc __read_mostly;
> int sysctl_tcp_early_retrans __read_mostly = 2;
>
> #define FLAG_DATA 0x01 /* Incoming frame contained data. */
> @@ -3608,15 +3607,6 @@ static int tcp_ack(struct sock *sk, cons
> if (after(ack, prior_snd_una))
> flag |= FLAG_SND_UNA_ADVANCED;
>
> - if (sysctl_tcp_abc) {
> - if (icsk->icsk_ca_state < TCP_CA_CWR)
> - tp->bytes_acked += ack - prior_snd_una;
> - else if (icsk->icsk_ca_state == TCP_CA_Loss)
> - /* we assume just one segment left network */
> - tp->bytes_acked += min(ack - prior_snd_una,
> - tp->mss_cache);
> - }
> -
> prior_fackets = tp->fackets_out;
> prior_in_flight = tcp_packets_in_flight(tp);
>
> --
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