Patchwork tcp: remove Appropriate Byte Count support

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.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

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On Tue, Feb 5, 2013 at 9:25 AM, Stephen Hemminger
<stephen@networkplumber.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@networkplumber.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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From: Yuchung Cheng <ycheng@google.com>
Date: Tue, 5 Feb 2013 09:47:59 -0800

> On Tue, Feb 5, 2013 at 9:25 AM, Stephen Hemminger
> <stephen@networkplumber.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@networkplumber.org>

Applied, and:

>>         tp->bytes_acked = 0;
> Is bytes_acked still needed?

I took care of this when I committed Stephen's patch.

Thanks.
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