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Message-ID: <CAK6E8=cmjY1HNhwx3rnXq3h3Gz2c5Mj7x_7LVg97bLwJ0EqeCw@mail.gmail.com>
Date:	Tue, 21 Jul 2015 23:50:07 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Lawrence Brakmo <brakmo@...com>
Cc:	netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [RFC PATCH v2 net-next 3/3] tcp: add NV congestion control

On Tue, Jul 21, 2015 at 9:21 PM, Lawrence Brakmo <brakmo@...com> wrote:
> This is a request for comments.
>
> TCP-NV (New Vegas) is a major update to TCP-Vegas. An earlier version of
> NV was presented at 2010's LPC (slides). It is a delayed based
> congestion avoidance for the data center. This version has been tested
> within a 10G rack where the HW RTTs are 20-50us.
>
> A description of TCP-NV, including implementation and experimental
> results, can be found at:
> http://www.brakmo.org/networking/tcp-nv/TCPNV.html
>
> The current version includes many module parameters to support
> experimentation with the parameters.
>
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
> ---
>  include/net/tcp.h          |   1 +
>  net/ipv4/Kconfig           |  16 ++
>  net/ipv4/Makefile          |   1 +
>  net/ipv4/sysctl_net_ipv4.c |   9 +
>  net/ipv4/tcp_input.c       |   2 +
>  net/ipv4/tcp_nv.c          | 479 +++++++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 508 insertions(+)
>  create mode 100644 net/ipv4/tcp_nv.c
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 2e62efe..c0690ae 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -281,6 +281,7 @@ extern unsigned int sysctl_tcp_notsent_lowat;
>  extern int sysctl_tcp_min_tso_segs;
>  extern int sysctl_tcp_autocorking;
>  extern int sysctl_tcp_invalid_ratelimit;
> +extern int sysctl_tcp_nv_enable;
>
>  extern atomic_long_t tcp_memory_allocated;
>  extern struct percpu_counter tcp_sockets_allocated;
> diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
> index 6fb3c90..c37b374 100644
> --- a/net/ipv4/Kconfig
> +++ b/net/ipv4/Kconfig
> @@ -539,6 +539,22 @@ config TCP_CONG_VEGAS
>         window. TCP Vegas should provide less packet loss, but it is
>         not as aggressive as TCP Reno.
>
> +config TCP_CONG_NV
> +       tristate "TCP NV"
> +       default m
> +       ---help---
> +       TCP NV is a follow up to TCP Vegas. It has been modified to deal with
> +       10G networks, measurement noise introduced by LRO, GRO and interrupt
> +       coalescence. In addition, it will decrease its cwnd multiplicative
multiplicatively

> +       instead of linearly.
> +
> +       Note that in general congestion avoidance (cwnd decreased when # packets
> +       queued grows) cannot coexist with congestion control (cwnd decreased only
> +       when there is packet loss) due to fairness issues. One scenario when the
s/the/they
> +       can coexist safely is when the CA flows have RTTs << CC flows RTTs.
> +
> +       For further details see http://www.brakmo.org/networking/tcp-nv/
> +
>  config TCP_CONG_SCALABLE
>         tristate "Scalable TCP"
>         default n
> diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
> index efc43f3..06f335f 100644
> --- a/net/ipv4/Makefile
> +++ b/net/ipv4/Makefile
> @@ -50,6 +50,7 @@ obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
>  obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
>  obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o
>  obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
> +obj-$(CONFIG_TCP_CONG_NV) += tcp_nv.o
>  obj-$(CONFIG_TCP_CONG_VENO) += tcp_veno.o
>  obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
>  obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index 433231c..31846d5 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -730,6 +730,15 @@ static struct ctl_table ipv4_table[] = {
>                 .proc_handler   = proc_dointvec_ms_jiffies,
>         },
>         {
> +               .procname       = "tcp_nv_enable",
> +               .data           = &sysctl_tcp_nv_enable,
> +               .maxlen         = sizeof(int),
> +               .mode           = 0644,
> +               .proc_handler   = proc_dointvec_minmax,
> +               .extra1         = &zero,
> +               .extra2         = &one,
> +       },
> +       {
>                 .procname       = "icmp_msgs_per_sec",
>                 .data           = &sysctl_icmp_msgs_per_sec,
>                 .maxlen         = sizeof(int),
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index aca4ae5..87560d9 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -101,6 +101,8 @@ int sysctl_tcp_thin_dupack __read_mostly;
>  int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
>  int sysctl_tcp_early_retrans __read_mostly = 3;
>  int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
> +int sysctl_tcp_nv_enable __read_mostly = 1;
> +EXPORT_SYMBOL(sysctl_tcp_nv_enable);
>
>  #define FLAG_DATA              0x01 /* Incoming frame contained data.          */
>  #define FLAG_WIN_UPDATE                0x02 /* Incoming ACK was a window update.       */
> diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c
> new file mode 100644
> index 0000000..af451b6
> --- /dev/null
> +++ b/net/ipv4/tcp_nv.c
> @@ -0,0 +1,479 @@
> +/*
> + * TCP NV: TCP with Congestion Avoidance
> + *
> + * TCP-NV is a successor of TCP-Vegas that has been developed to
> + * deal with the issues that occur in modern networks.
> + * Like TCP-Vegas, TCP-NV supports true congestion avoidance,
> + * the ability to detect congestion before packet losses occur.
> + * When congestion (queue buildup) starts to occur, TCP-NV
> + * predicts what the cwnd size should be for the current
> + * throughput and it reduces the cwnd proportionally to
> + * the difference between the current cwnd and the predicted cwnd.
> + * TCP-NV behaves like Reno when no congestion is detected, or when
> + * recovering from packet losses.
what happens when loss is not related to congestion?
> + *
> + * TODO:
> + * 1) Modify the behavior so cwnd can grow faster under certain conditions
> + * 2) Add mechanism to deal with reverse congestion.
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/math64.h>
> +#include <net/tcp.h>
> +#include <linux/inet_diag.h>
> +
> +/* TCP NV parameters */
> +static int nv_pad __read_mostly = 10;
> +static int nv_pad_buffer __read_mostly = 2;
> +static int nv_reset_period __read_mostly = 5;
> +static int nv_min_cwnd = 10;
> +static int nv_dec_eval_min_calls = 100;
> +static int nv_ssthresh_eval_min_calls = 30;
> +static int nv_rtt_min_cnt = 2;
> +static int nv_cong_decrease_mult = 30*128/100;
> +static int nv_ssthresh_factor = 8;
> +static int nv_rtt_factor = 128;
> +static int nv_rtt_cnt_dec_delta = 20; /* dec cwnd by this many RTTs */
> +static int nv_dec_factor = 5;  /* actual value is factor/8 */
> +static int nv_loss_dec_factor = 820; /* on loss reduce cwnd by 20% */
> +static int nv_cwnd_growth_factor = 2; /* larger => cwnd grows slower */
> +
> +module_param(nv_pad, int, 0644);
> +MODULE_PARM_DESC(nv_pad, "extra packets above congestion level");
> +module_param(nv_pad_buffer, int, 0644);
> +MODULE_PARM_DESC(nv_pad_buffer, "no growth buffer zone");
> +module_param(nv_reset_period, int, 0644);
> +MODULE_PARM_DESC(nv_reset_period, "nv_min_rtt reset period (secs)");
> +module_param(nv_min_cwnd, int, 0644);
> +MODULE_PARM_DESC(nv_min_cwnd, "NV will not decrease cwnd below this value"
> +                " without losses");
> +module_param(nv_dec_eval_min_calls, int, 0644);
> +MODULE_PARM_DESC(nv_dec_eval_min_calls, "Wait for this many data points "
> +                "before declaring congestion (< 256)");
> +module_param(nv_ssthresh_eval_min_calls, int, 0644);
> +MODULE_PARM_DESC(nv_ssthresh_eval_min_calls, "Wait for this many data points "
> +                "before declaring congestion during initial slow-start");
> +module_param(nv_rtt_min_cnt, int, 0644);
> +MODULE_PARM_DESC(nv_rtt_min_cnt, "Wait for this many RTTs before declaring"
> +                " congestion (<64)");
> +module_param(nv_cong_decrease_mult, int, 0644);
> +MODULE_PARM_DESC(nv_cong_decrease_mult, "Congestion decrease factor");
> +module_param(nv_ssthresh_factor, int, 0644);
> +MODULE_PARM_DESC(nv_ssthresh_factor, "ssthresh factor");
> +module_param(nv_rtt_factor, int, 0644);
> +MODULE_PARM_DESC(nv_rtt_factor, "rtt averaging factor (0-256)");
> +module_param(nv_rtt_cnt_dec_delta, int, 0644);
> +MODULE_PARM_DESC(nv_rtt_cnt_dec_delta, "decrease cwnd for this many RTTs "
> +                "every 100 RTTs");
> +module_param(nv_dec_factor, int, 0644);
> +MODULE_PARM_DESC(nv_dec_factor, "decrease cwnd every ~192 RTTS by factor/8");
> +module_param(nv_loss_dec_factor, int, 0644);
> +MODULE_PARM_DESC(nv_loss_dec_factor, "on loss new cwnd = cwnd * this / 1024");
> +module_param(nv_cwnd_growth_factor, int, 0644);
> +MODULE_PARM_DESC(nv_cwnd_growth_factor, "larger => cwnd grows slower");
> +
> +/* TCP NV Parameters */
> +struct tcpnv {
> +       unsigned long nv_min_rtt_reset_jiffies;  /* when to switch to
> +                                                 * nv_min_rtt_new */
> +       u32 cnt;                /* increase cwnd by 1 after ACKs */
> +       u32 loss_cwnd;  /* cwnd at last loss */
> +       u8  nv_enable:1,
> +               nv_allow_cwnd_growth:1,         /* whether cwnd can grow */
> +               nv_rtt_cnt:6;   /* RTTs without making ca decision */
> +       u8  nv_eval_call_cnt;/* call count since last eval */
> +       u8  nv_min_cwnd;        /* nv won't make a ca decision if cwnd is
> +                                * smaller than this. It may grow to handle
> +                                * TSO, LRO and interrupt coalescence because
> +                                * with these a small cwnd cannot saturate
> +                                * the link. Note that this is different from
> +                                * sysctl_tcp_nv_min_cwnd */
> +       u8  available;
> +       u32 nv_last_rtt;        /* last rtt */
> +       u32 nv_min_rtt;         /* active min rtt. Used to determine slope */
> +       u32 nv_min_rtt_new;     /* min rtt for future use */
> +       u32 nv_rtt_max_rate;    /* max rate seen during current RTT */
> +       u32 nv_rtt_start_seq;   /* current RTT ends when packet arrives
> +                                * acking beyond nv_rtt_start_seq */
> +       u32 nv_last_snd_una;    /* Previous value of tp->snd_una. It is
> +                                * used to determine bytes acked since last
> +                                * call to bictcp_acked */
> +       u32 nv_no_cong_cnt;     /* Consecutive no congestion decisions */
> +       u32 nv_rtt_cnt_dec;     /* RTTs since last temporary cwnd decrease */
> +};
> +
> +#define NV_INIT_RTT      0xffffffff
> +#define NV_MIN_CWND      4
> +#define NV_MIN_CWND_GROW  2
> +#define NV_TSO_CWND_BOUND 80
> +
> +static inline void tcpnv_reset(struct tcpnv *ca, struct sock *sk)
> +{
> +       struct tcp_sock *tp = tcp_sk(sk);
> +
> +       ca->loss_cwnd = 0;
> +       ca->nv_no_cong_cnt = 0;
> +       ca->cnt = 0;
> +       ca->nv_rtt_cnt = 0;
> +       ca->nv_rtt_cnt_dec = 0;
> +       ca->nv_allow_cwnd_growth = 1;
> +       ca->nv_last_rtt = 0;
> +       ca->nv_rtt_max_rate = 0;
> +       ca->nv_rtt_start_seq = tp->snd_una;
> +       ca->nv_eval_call_cnt = 0;
> +       ca->nv_last_snd_una = tp->snd_una;
> +}
> +
> +static void tcpnv_init(struct sock *sk)
> +{
> +       struct tcpnv *ca = inet_csk_ca(sk);
> +
> +       tcpnv_reset(ca, sk);
> +
> +       ca->nv_min_rtt_reset_jiffies = jiffies + 2*HZ;
> +       ca->nv_min_rtt = NV_INIT_RTT;
> +       ca->nv_min_rtt_new = NV_INIT_RTT;
> +       ca->nv_enable = sysctl_tcp_nv_enable;
> +       ca->nv_min_cwnd = NV_MIN_CWND;
> +       if (nv_dec_eval_min_calls > 255)
> +               nv_dec_eval_min_calls = 255;
> +       if (nv_rtt_min_cnt > 63)
> +               nv_rtt_min_cnt = 63;
> +}
> +
> +static void tcpnv_cong_avoid(struct sock *sk, u32 ack, u32 acked)
> +{
> +       struct tcp_sock *tp = tcp_sk(sk);
> +       struct tcpnv *ca = inet_csk_ca(sk);
> +
> +       if (!tcp_is_cwnd_limited(sk))
> +               return;
> +
> +       /* Only grow cwnd if NV has not detected congestion */
> +       if (sysctl_tcp_nv_enable && ca->nv_enable &&
> +           !ca->nv_allow_cwnd_growth)
> +               return;
> +
> +       if (tp->snd_cwnd <= tp->snd_ssthresh) {
> +               acked = tcp_slow_start(tp, acked);
> +               if (!acked)
> +                       return;
> +       }
> +       if (ca->cnt == 0 || !(sysctl_tcp_nv_enable || ca->nv_enable))
> +               ca->cnt = tp->snd_cwnd;
> +
> +       tcp_cong_avoid_ai(tp, ca->cnt, acked);
> +}
> +
> +static u32 tcpnv_recalc_ssthresh(struct sock *sk)
> +{
> +       const struct tcp_sock *tp = tcp_sk(sk);
> +       struct tcpnv *ca = inet_csk_ca(sk);
> +
> +       ca->loss_cwnd = tp->snd_cwnd;
> +       return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
> +}
> +
> +static u32 tcpnv_undo_cwnd(struct sock *sk)
> +{
> +       struct tcpnv *ca = inet_csk_ca(sk);
> +
> +       return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
> +}
> +
> +static void tcpnv_state(struct sock *sk, u8 new_state)
> +{
> +       struct tcpnv *ca = inet_csk_ca(sk);
> +
> +       if (new_state == TCP_CA_Open) {
> +               ca->nv_enable = 1;
> +               tcpnv_reset(ca, sk);
> +       } else if (new_state == TCP_CA_Loss) {
> +               ca->nv_enable = 0;
> +       }
> +}
> +
> +/* Do congestion avoidance calculaitons for TCP-NV
> + */
> +static void tcpnv_acked(struct sock *sk, struct ack_sample sample)
> +{
> +       const struct inet_connection_sock *icsk = inet_csk(sk);
> +       struct tcp_sock *tp = tcp_sk(sk);
> +       struct tcpnv *ca = inet_csk_ca(sk);
> +       unsigned long now = jiffies;
> +       s64 rate64 = 0;
> +       u32 rate, max_win, cwnd_by_slope;
> +       u32 avg_rtt;
> +       u32 bytes_acked = 0;
> +
> +       /* Some calls are for duplicates without timetamps */
> +       if (sample.rtt_us < 0)
> +               return;
> +
> +       /* If not in TCP_CA_Open state, skip. */
> +       if (icsk->icsk_ca_state != TCP_CA_Open)
> +               return;
> +
> +       /* If NV mode is not enabled, behave like Reno */
> +       if (!sysctl_tcp_nv_enable  ||  !ca->nv_enable) {
> +               ca->nv_allow_cwnd_growth = 1;
what's the use case of using NV with sysctl_tcp_nv_enable=0?

> +               return;
> +       }
> +
> +       bytes_acked = tp->snd_una - ca->nv_last_snd_una;
> +       ca->nv_last_snd_una = tp->snd_una;
> +
> +       if (sample.in_flight == 0)
> +               return;
> +
> +       /* Calculate moving average of RTT */
> +       if (nv_rtt_factor > 0) {
> +               if (ca->nv_last_rtt > 0) {
> +                       avg_rtt = (((u64)sample.rtt_us) * nv_rtt_factor +
> +                                  ((u64)ca->nv_last_rtt)
> +                                  * (256 - nv_rtt_factor)) >> 8;
> +               } else {
> +                       avg_rtt = sample.rtt_us;
> +                       ca->nv_min_rtt = avg_rtt << 1;
> +               }
> +               ca->nv_last_rtt = avg_rtt;
> +       } else {
> +               avg_rtt = sample.rtt_us;
> +       }
> +
> +       /* rate in 100's bits per second */
> +       rate64 = ((u64)sample.in_flight) * 8000000;
> +       rate = (u32)div64_u64(rate64, (u64)(avg_rtt*100));
> +
> +       /* Remember the maximum rate seen during this RTT
> +        * Note: It may be more than one RTT. This function should be
> +        *       called at least nv_dec_eval_min_calls times.
> +        */
> +       if (ca->nv_rtt_max_rate < rate)
> +               ca->nv_rtt_max_rate = rate;
> +
> +       /* We have valid information, increment counter */
> +       if (ca->nv_eval_call_cnt < 255)
> +               ca->nv_eval_call_cnt++;
> +
> +       /* update min rtt if necessary */
> +       if (avg_rtt < ca->nv_min_rtt)
> +               ca->nv_min_rtt = avg_rtt;
> +
> +       /* update future min_rtt if necessary */
> +       if (avg_rtt < ca->nv_min_rtt_new)
> +               ca->nv_min_rtt_new = avg_rtt;
> +
> +       /* nv_min_rtt is updated with the minimum (possibley averaged) rtt
> +        * seen in the last sysctl_tcp_nv_reset_period seconds (i.e. a
> +        * warm reset). This new nv_min_rtt will be continued to be updated
> +        * and be used for another sysctl_tcp_nv_reset_period seconds,
> +        * when it will be updated again.
> +        * In practice we introduce some randomness, so the actual period used
> +        * is chosen randomly from the range:
> +        *   [sysctl_tcp_nv_reset_period*3/4, sysctl_tcp_nv_reset_period*5/4)
> +        */
> +       if (time_after_eq(now, ca->nv_min_rtt_reset_jiffies)) {
> +               unsigned char rand;
> +               ca->nv_min_rtt = ca->nv_min_rtt_new;
> +               ca->nv_min_rtt_new = NV_INIT_RTT;
> +               get_random_bytes(&rand, 1);
> +               ca->nv_min_rtt_reset_jiffies =
> +                       now + ((nv_reset_period*(384 + rand)*HZ)>>9);
> +               /* Every so often we decrease nv_min_cwnd in case previous
> +                *  value is no longer accurate.
> +                */
> +               ca->nv_min_cwnd = max(ca->nv_min_cwnd/2, NV_MIN_CWND);
> +       }
> +
> +       /* Once per RTT check if we need to do congestion avoidance */
> +       if (before(ca->nv_rtt_start_seq, tp->snd_una)) {
> +               ca->nv_rtt_start_seq = tp->snd_nxt;
> +               if (ca->nv_rtt_cnt < 63)
> +                       /* Increase counter for RTTs without CA decision */
> +                       ca->nv_rtt_cnt++;
> +               if (ca->nv_rtt_cnt_dec < 255)
> +                       /* Increase counter for temporary cwnd decrease */
> +                       ca->nv_rtt_cnt_dec++;
> +
> +               /* If this function is only called once within an RTT
> +                * the cwnd is probably too small (in some cases due to
> +                * tso, lro or interrupt coalescence), so we increase
> +                * nv_min_cwnd.
> +                */
> +               if (ca->nv_eval_call_cnt == 1
> +                   && bytes_acked >= (ca->nv_min_cwnd - 1) * tp->mss_cache
> +                   && ca->nv_min_cwnd < (NV_TSO_CWND_BOUND + 1)
> +                   && ca->nv_rtt_cnt_dec < 192) {
> +                       ca->nv_min_cwnd = min(ca->nv_min_cwnd
> +                                             + NV_MIN_CWND_GROW,
> +                                             NV_TSO_CWND_BOUND + 1);
> +                       ca->nv_rtt_start_seq = tp->snd_nxt +
> +                               ca->nv_min_cwnd*tp->mss_cache;
> +                       ca->nv_eval_call_cnt = 0;
> +                       ca->nv_allow_cwnd_growth = 1;
> +                       return;
> +               }
> +
> +               /* Every 192 to 320 RTTs decrease cwnd to get better min RTT
> +                * measurement. In practice we accomplish this by initializing
> +                * nv_rtt_cnd_dec randomly form the range [0, 128) and
> +                * stopping at 320.
> +                * We keep the value low for nv_rtt_cnt_dec_delta RTTs and then
> +                * we restore cwnd to its previous value (by setting
> +                * ssthresh to the previous value).
> +                */
> +               if (ca->nv_rtt_cnt_dec == 320) {
> +                       /* decrease cwnd and ssthresh */
> +                       tp->snd_cwnd =
> +                               max((unsigned int)nv_min_cwnd,
> +                                   ((tp->snd_cwnd * nv_dec_factor) >> 3));
> +                       tp->snd_ssthresh =
> +                               max(tp->snd_cwnd,
> +                                   ((tp->snd_ssthresh * nv_dec_factor) >> 3));
> +                       ca->nv_allow_cwnd_growth = 0;
> +                       return;
> +               } else if (ca->nv_rtt_cnt_dec > 320) {
> +                       if (ca->nv_rtt_cnt_dec - 320 >= nv_rtt_cnt_dec_delta) {
> +                               /* Restore ssthresh to restore cwnd */
> +                               unsigned char rand;
> +                               get_random_bytes(&rand, 1);
> +                               ca->nv_rtt_cnt_dec = rand >> 1;
> +                               tp->snd_ssthresh = (tp->snd_ssthresh << 3)
> +                                       / nv_dec_factor;
> +                               ca->nv_allow_cwnd_growth = 1;
> +                               ca->nv_no_cong_cnt = 0;
> +                       }
> +                       return;
> +               }
> +
> +               /* Find the ideal cwnd for current rate from slope
> +                * slope = 80000.0 * mss / nv_min_rtt
> +                * cwnd_by_slope = nv_rtt_max_rate / slope
> +                */
> +               cwnd_by_slope = (u32)
> +                       div64_u64(((u64)ca->nv_rtt_max_rate) * ca->nv_min_rtt,
> +                                 (u64)(80000 * tp->mss_cache));
> +               max_win = cwnd_by_slope + nv_pad;
> +
> +               /* If cwnd > max_win, decrease cwnd
> +                * if cwnd < max_win, grow cwnd
> +                * else leave the same
> +                */
> +               if (tp->snd_cwnd > max_win) {
> +                       /* there is congestion, check that it is ok
> +                        * to make a CA decision
> +                        * 1. We should have at least nv_dec_eval_min_calls
> +                        *    data points before making a CA  decision
> +                        * 2. We only make a congesion decision after
> +                        *    nv_rtt_min_cnt RTTs
> +                        */
> +                       if (ca->nv_rtt_cnt < nv_rtt_min_cnt)
> +                               return;
> +                       else if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) {
> +                               if (ca->nv_eval_call_cnt <
> +                                   nv_ssthresh_eval_min_calls)
> +                                       return;
> +                       } else if (ca->nv_eval_call_cnt <
> +                                  nv_dec_eval_min_calls) {
> +                               return;
> +                       }
> +
> +                       /* We have enough data to determine we are congested */
> +                       ca->nv_allow_cwnd_growth = 0;
> +                       tp->snd_ssthresh =
> +                               (nv_ssthresh_factor * max_win) >> 3;
> +                       if (tp->snd_cwnd - max_win > 2) {
> +                               /* gap > 2, we do exponential cwnd decrease */
> +                               int dec;
> +                               dec = max(2U, ((tp->snd_cwnd - max_win) *
> +                                              nv_cong_decrease_mult) >> 7);
> +                               tp->snd_cwnd -= dec;
> +                       } else if (nv_cong_decrease_mult > 0) {
> +                               tp->snd_cwnd = max_win;
> +                       }
> +                       ca->cnt = tp->snd_cwnd;
> +                       ca->nv_no_cong_cnt = 0;
> +               } else if (tp->snd_cwnd <=  max_win - nv_pad_buffer) {
> +                       /* We allow growth of cwnd every RTT since we would
> +                        * have grown even if we waited (just slower)
> +                        */
> +                       ca->nv_allow_cwnd_growth = 1;
> +                       ca->nv_no_cong_cnt++;
> +                       if (nv_cwnd_growth_factor > 0 &&
> +                           ca->nv_no_cong_cnt > nv_cwnd_growth_factor) {
> +                               ca->cnt = max(ca->cnt >> 1, (u32) 4);
> +                               ca->nv_no_cong_cnt = 0;
> +                       }
> +               } else {
> +                       ca->nv_allow_cwnd_growth = 0;
> +               }
> +
> +               /* update state */
> +               ca->nv_eval_call_cnt = 0;
> +               ca->nv_rtt_cnt = 0;
> +               ca->nv_rtt_max_rate = 0;
> +
> +               /* Don't want to make cwnd < nv_min_cwnd
> +                * (it wasn't before, if it is now is because nv
> +                *  decreased it).
> +                */
> +               if (tp->snd_cwnd < nv_min_cwnd)
> +                       tp->snd_cwnd = nv_min_cwnd;
> +
> +  }
> +}
> +
> +/* Extract info for Tcp socket info provided via netlink */
> +size_t tcpnv_get_info(struct sock *sk, u32 ext, int *attr,
> +                      union tcp_cc_info *info)
> +{
> +       const struct tcpnv *ca = inet_csk_ca(sk);
> +
> +       if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
> +               info->vegas.tcpv_enabled = ca->nv_enable
> +                       && sysctl_tcp_nv_enable;
> +               info->vegas.tcpv_rttcnt = ca->nv_rtt_cnt;
> +               info->vegas.tcpv_rtt = ca->nv_last_rtt;
> +               info->vegas.tcpv_minrtt = ca->nv_min_rtt;
> +
> +               *attr = INET_DIAG_VEGASINFO;
> +               return sizeof(struct tcpvegas_info);
> +       }
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(tcpnv_get_info);
> +
> +static struct tcp_congestion_ops tcpnv __read_mostly = {
> +       .init           = tcpnv_init,
> +       .ssthresh       = tcpnv_recalc_ssthresh,
> +       .cong_avoid     = tcpnv_cong_avoid,
> +       .set_state      = tcpnv_state,
> +       .undo_cwnd      = tcpnv_undo_cwnd,
> +       .pkts_acked     = tcpnv_acked,
> +       .get_info       = tcpnv_get_info,
> +
> +       .owner          = THIS_MODULE,
> +       .name           = "nv",
> +};
> +
> +static int __init tcpnv_register(void)
> +{
> +       BUILD_BUG_ON(sizeof(struct tcpnv) > ICSK_CA_PRIV_SIZE);
> +
> +       return tcp_register_congestion_control(&tcpnv);
> +}
> +
> +static void __exit tcpnv_unregister(void)
> +{
> +       tcp_unregister_congestion_control(&tcpnv);
> +}
> +
> +module_init(tcpnv_register);
> +module_exit(tcpnv_unregister);
> +
> +MODULE_AUTHOR("Lawrence Brakmo");
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("TCP NV");
> +MODULE_VERSION("1.0");
> --
> 1.8.1
>
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