我对TCP CDG拥塞控制算法的改进和优化

其实这不是我的优化，我是借用了BBR之力。         借了什么力呢？这是我一再强调的，BBR最大的共享不是为Linux贡献了一个TCP拥塞控制算法(它同时在也BSD上被实现...)，而是它重构了Linux TCP的实现！借助BBR对Linux TCP实现的重构，很多之前做不到的事情，现在可以做到了。         简而言之，BBR算法对Linux TCP实现的重构中，将以下三件事完全分离： 1.重传哪些包； 2.传输多少包； 3.实际传输。 拥塞控制算法侧重解决上述第2点问题。 ----------------------------------- CDG必须要拥塞窗口的背后默默维护一个”自己的窗口“，称为shadow_wnd，该窗口只受”实际拥塞情况“的影响，而不受”Linux TCP拥塞状态机“的影响。所以说，即便在丢包重传的Recovery时期，也必须动态维护这个shadow_wnd，使其按照Reno方式增长(或者按照CUBIC方式，随便什么方式都可以)。         然则这在BBR之前的Linux 4.8版本之前的内核中是无法做到的。因为tcp_congestion_ops机构体中没有一个回调函数是在Recovery阶段可以被调用的到的，而你所能控制的拥塞算法只能通过tcp_congestion_ops结构体的回调来实现。 BBR将以下的逻辑引入到了Linux： [plain] view plain copy 在CODE上查看代码片派生到我的代码片 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,                   int flag, const struct rate_sample *rs)  {      const struct inet_connection_sock *icsk = inet_csk(sk);        if (icsk->icsk_ca_ops->cong_control) {          icsk->icsk_ca_ops->cong_control(sk, rs);          return;      }        if (tcp_in_cwnd_reduction(sk)) {          /* Reduce cwnd if state mandates */          tcp_cwnd_reduction(sk, acked_sacked, flag);      } else if (tcp_may_raise_cwnd(sk, flag)) {          /* Advance cwnd if state allows */          tcp_cong_avoid(sk, ack, acked_sacked);      }      tcp_update_pacing_rate(sk);  }

只要实现了cong_control回调，那就就不会再调用标准的PRR算法和拥塞避免tcp_cong_avoid函数，无论在任何阶段，均调用cong_control回调。因此，我的方法是，在Recovery或者Loss状态调用cong_control回调即可！在该回调中维护CDG的shadow窗口。         这谈何容易！BBR引入的逻辑非常粗糙，只要实现了cong_control，该函数就无条件返回。事实上正确的做法是cong_control回调有个返回值，当满足一定条件时返回，否则继续下面的逻辑。但是BBR并没有引入这些。 ----------------------------------- 但是，我将其引入了。         请看，我将tcp_input.c中的tcp_cong_control改成了下面的样子： [plain] view plain copy 在CODE上查看代码片派生到我的代码片 static void tcp_cong_control(struct sock *sk, u32 ack, u32 prior_in_flight, u32 acked_sacked,                                               int flag, const struct rate_sample *rs)  {          const struct inet_connection_sock *icsk = inet_csk(sk);  #ifdef BBR          if (icsk->icsk_ca_ops->cong_control) {                  icsk->icsk_ca_ops->cong_control(sk, rs);  #ifdef CDG                  // 以下是我添加的判断，新增了rs的flag字段，一旦置位就继续而不返回。                  if (!(rs->flag & CDG_CONT))                          return;  #endif          }  #endif          if (tcp_in_cwnd_reduction(sk)) {          /* Reduce cwnd if state mandates */                  tcp_cwnd_reduction(sk, acked_sacked, 1);          } else if (tcp_may_raise_cwnd(sk, flag)) {                  /* Advance cwnd if state allows */                  tcp_cong_avoid(sk, ack, prior_in_flight);          }          tcp_update_pacing_rate(sk);  }  我添加了个判断。其实我的目的很简单，就是在Recovery状态下也能调用到CDG的逻辑，就这么简单个逻辑在不懂的人眼里显得如此高大上，在懂的人眼里显得如此傻逼...不管怎样，我做了。 ----------------------------------- 以下的代码只是我对标准Linux 4.3内核CDG算法的differ，想理解代码细节的，请先阅读标准CDG代码，我虽然是个传说中有求必应的人，但那只是传说...请注意，我的目标内核是3.10内核，在我移植CDG之前，我已经移植了BBR，所以说，你最好以4.9内核为准，然而这样一来，又会对3.10内核的一些接口表示费解..这里不就不多解释了，我要说的是，想彻底逃离学院派，就必须把所有这些代码都搞清楚！不然的话，首先，你根本什么都看不懂，其次，即便你有想法，你也做不来。完整的代码我会附在本文最后。 以下是patch中几个重要函数的说明： 1.CDG的cong_control回调函数cdg_main： [plain] view plain copy 在CODE上查看代码片派生到我的代码片 static void cdg_main(struct sock *sk, struct rate_sample *rs)  {          struct inet_connection_sock *icsk = inet_csk(sk);          struct tcp_sock *tp = tcp_sk(sk);          struct cdg *ca = inet_csk_ca(sk);            if (!shadow_grow) {                  rs->flag |= CDG_CONT;                  return;          }            if (icsk->icsk_ca_state != TCP_CA_Open) {                  // 在重传阶段，依然要采集rtt，因为链路不问包类型，重传包也会影响网络可用容量。                  if (rs->rtt_us) {                          // 感谢BBR增加了rs结构体，从中可以取rtt_us                          ca->rtt.min = min_not_zero(ca->rtt.min, (s32)rs->rtt_us);                          ca->rtt.max = max(ca->rtt.max, (s32)rs->rtt_us);                  }                    if (ca->state == CDG_NONFULL && use_tolerance) {                          if (!shadow_fast && (ca->ack_sack_cnt < 0 || ca->ack_sack_cnt == 0) && ca->rtt.v64) {                                  s32 grad = 0;                                    if (ca->rtt_prev.v64)                                          grad = tcp_cdg_grad(ca);                                  ca->rtt_prev = ca->rtt;                                  ca->ack_sack_cnt = tcp_packets_in_flight(tp);                                  ca->rtt.v64 = 0;                          }                          ca->ack_sack_cnt -= rs->acked_sacked;                          if (ca->state == CDG_NONFULL || shadow_fast) {                                  // 如果链路未完全拥塞，那么shadow窗口便默默地帮助实际窗口占据空间，等到快速恢复结束，便可以由实际窗口可用。                                  tcp_cong_avoid_ai_shadow(sk, ca->shadow_wnd, rs->acked_sacked);                                  tp->snd_cwnd = ca->shadow_wnd;                          }                            rs->flag |= CDG_CONT;                  }          } else {                  // 为了让执行流继续，增加CDG_CONT标志。                  rs->flag |= CDG_CONT;          }  }

2.状态设置回调函数cdg_state： [plain] view plain copy 在CODE上查看代码片派生到我的代码片 static void cdg_state(struct sock *sk, u8 new_state)  {          struct cdg *ca = inet_csk_ca(sk);          struct tcp_sock *tp = tcp_sk(sk);            if (!recovery_restore)                  return;          if (new_state == TCP_CA_Open)                  // 进入Open状态时，直接接管shadow窗口，这里可能会有突发问题。                  tp->snd_cwnd = max(max(tp->snd_cwnd, ca->shadow_wnd), 2U);          if (new_state == TCP_CA_Loss) {                  // 进入Loss状态，判断是否是噪声丢包                  if (ca->state == CDG_NONFULL && use_tolerance) {                          // 如果是噪声丢包，那么便恢复窗口。                          tp->snd_cwnd = ca->shadow_wnd;                          printk("#### cwnd:%u \n", tp->snd_cwnd);                          if (loss_push)                                  // 如果是噪声丢包，那么在窗口内继续发送数据。                                  tcp_push_pending_frames(sk);                  }                  // 如果是拥塞丢包，那么执行原有流程。          }  }

3.UNDO函数tcp_cdg_undo_cwnd： [plain] view plain copy 在CODE上查看代码片派生到我的代码片 static u32 tcp_cdg_undo_cwnd(struct sock *sk)  {          struct cdg *ca = inet_csk_ca(sk);          struct tcp_sock *tp = tcp_sk(sk);          // undo到shadow窗口          return max3(2U, ca->shadow_wnd, max(tp->snd_cwnd, ca->undo_cwnd));  }

4.RTT梯度计算函数tcp_cdg_grad： [plain] view plain copy 在CODE上查看代码片派生到我的代码片 static s32 tcp_cdg_grad(struct cdg *ca)  {          // rtt在pkts_acked回调和cong_control中被采样值更新          s32 gmin = ca->rtt.min - ca->rtt_prev.min;          s32 gmax = ca->rtt.max - ca->rtt_prev.max;          s32 grad;            if (ca->gradients) {                  ca->gsum.min += gmin - ca->gradients[ca->tail].min;                  ca->gsum.max += gmax - ca->gradients[ca->tail].max;                  ca->gradients[ca->tail].min = gmin;                  ca->gradients[ca->tail].max = gmax;                  ca->tail = (ca->tail + 1) & (window - 1);                  gmin = ca->gsum.min;                  gmax = ca->gsum.max;          }          ......          /* Backoff was effectual: */          if (gmin <= -32 || gmax <= -32)                  ca->backoff_cnt = 0;            if (use_tolerance) {                  /* Reduce small variations to zero: */                  gmin = DIV_ROUND_CLOSEST(gmin, 64);                  gmax = DIV_ROUND_CLOSEST(gmax, 64);                  // 注意看上一篇文章CDG模型图示的边沿触发条件。                  if (gmin > 0 && gmax <= 0)                          ca->state = CDG_FULL;                  else if ((gmin > 0 && gmax > 0) || gmax < 0)                          ca->state = CDG_NONFULL;          }          return grad;  }

我首先盲测了一下原生的CDG，Oh NO！太垃圾，比CUBIC好，高丢包率下竟然与Westwood相当，在所有这一切中，BBR始终是另类，遥不可及，在我看了Paper之后，迅速自己实现了一版，感谢BBR对Linux TCP的重构！我承认我自己只懂Reno，BIC，CUBIC，Vegas，BBR这几种算法，其它HTCP，Westwood这些我并没有详细分析过，但是无论我怎么测，我发现我的CDG(应该是我改过的CDG)，一直跟BBR接近。         CDG是什么？CDG实际上就是传统基于丢包的算法加上了一个抗噪声机制，本来基于丢包的算法就是以不断填充缓存为手段，直到填满缓存发生丢包进行减窗，然而有的时候并非拥塞的原因也会发生丢包，此时按照算法来看依然会减窗，这就大大降低了带宽的利用率。加上了这个CDG的RTT梯度抗噪声机制后，网络带宽的利用率大大提高了。然而可能会加重拥塞，所以CDG内置了backoff算法，这里就不赘述了。 ----------------------------------- tcp_cdg.c代码：

[plain] view plain copy 在CODE上查看代码片派生到我的代码片 #include <linux/kernel.h>  #include <linux/random.h>  #include <linux/module.h>  #include <net/tcp.h>    #define HYSTART_ACK_TRAIN   1  #define HYSTART_DELAY       2    static int window __read_mostly = 8;  static unsigned int backoff_beta __read_mostly = 0.7071 * 1024; /* sqrt 0.5 */  static unsigned int backoff_factor __read_mostly = 42;  static unsigned int hystart_detect __read_mostly = 3;  static unsigned int use_ineff __read_mostly = 5;  static unsigned int use_shadow __read_mostly = 1;  static unsigned int backoff __read_mostly = 0;  static unsigned int use_tolerance __read_mostly = 1;  static unsigned int shadow_fast __read_mostly = 1;  static unsigned int shadow_grow __read_mostly = 1;  static unsigned int recovery_restore __read_mostly = 1;  static unsigned int loss_push __read_mostly = 1;    module_param(window, int, 0444);  MODULE_PARM_DESC(window, "gradient window size (power of two <= 256)");  module_param(backoff_beta, uint, 0644);  MODULE_PARM_DESC(backoff_beta, "backoff beta (0-1024)");  module_param(backoff_factor, uint, 0644);  MODULE_PARM_DESC(backoff_factor, "backoff probability scale factor");  module_param(hystart_detect, uint, 0644);  MODULE_PARM_DESC(hystart_detect, "use Hybrid Slow start "           "(0: disabled, 1: ACK train, 2: delay threshold, 3: both)");  module_param(use_ineff, uint, 0644);  MODULE_PARM_DESC(use_ineff, "use ineffectual backoff detection (threshold)");  module_param(use_shadow, uint, 0644);  MODULE_PARM_DESC(use_shadow, "use shadow window heuristic");  module_param(backoff, uint, 0644);  MODULE_PARM_DESC(backoff, "back");  module_param(use_tolerance, uint, 0644);  MODULE_PARM_DESC(use_tolerance, "use loss tolerance heuristic");  module_param(shadow_fast, uint, 0644);  MODULE_PARM_DESC(shadow_fast, "back");  module_param(shadow_grow, uint, 0644);  MODULE_PARM_DESC(shadow_grow, "back");  module_param(recovery_restore, uint, 0644);  MODULE_PARM_DESC(recovery_restore, "back");  module_param(loss_push, uint, 0644);  MODULE_PARM_DESC(loss_push, "back");    struct cdg_minmax {      union {          struct {              s32 min;              s32 max;          };          u64 v64;      };  };    enum cdg_state {      CDG_UNKNOWN = 0,      CDG_NONFULL = 1,      CDG_FULL    = 2,      CDG_BACKOFF = 3,  };    struct cdg {      struct cdg_minmax rtt;      struct cdg_minmax rtt_prev;      struct cdg_minmax *gradients;      struct cdg_minmax gsum;      bool gfilled;      u8  tail;      u8  state;      u8  delack;      u32 rtt_seq;      u32 undo_cwnd;      u32 shadow_wnd;      u32 snd_cwnd_cnt;      u16 backoff_cnt;      u16 sample_cnt;      s32 delay_min;      s32 ack_sack_cnt;      u32 last_ack;      u32 round_start;  };    /**   * nexp_u32 - negative base-e exponential   * @ux: x in units of micro   *   * Returns exp(ux * -1e-6) * U32_MAX.   */  static u32 __pure nexp_u32(u32 ux)  {      static const u16 v[] = {          /* exp(-x)*65536-1 for x = 0, 0.000256, 0.000512, ... */          65535,          65518, 65501, 65468, 65401, 65267, 65001, 64470, 63422,          61378, 57484, 50423, 38795, 22965, 8047,  987,   14,      };      u32 msb = ux >> 8;      u32 res;      int i;        /* Cut off when ux >= 2^24 (actual result is <= 222/U32_MAX). */      if (msb > U16_MAX)          return 0;        /* Scale first eight bits linearly: */      res = U32_MAX - (ux & 0xff) * (U32_MAX / 1000000);        /* Obtain e^(x + y + ...) by computing e^x * e^y * ...: */      for (i = 1; msb; i++, msb >>= 1) {          u32 y = v[i & -(msb & 1)] + U32_C(1);            res = ((u64)res * y) >> 16;      }        return res;  }    /* Based on the HyStart algorithm (by Ha et al.) that is implemented in   * tcp_cubic. Differences/experimental changes:   *   o Using Hayes' delayed ACK filter.   *   o Using a usec clock for the ACK train.   *   o Reset ACK train when application limited.   *   o Invoked at any cwnd (i.e. also when cwnd < 16).   *   o Invoked only when cwnd < ssthresh (i.e. not when cwnd == ssthresh).   */  static void tcp_cdg_hystart_update(struct sock *sk)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);        ca->delay_min = min_not_zero(ca->delay_min, ca->rtt.min);      if (ca->delay_min == 0)          return;        if (hystart_detect & HYSTART_ACK_TRAIN) {          u32 now_us = div_u64(local_clock(), NSEC_PER_USEC);            if (ca->last_ack == 0 || !tcp_is_cwnd_limited(sk, tcp_packets_in_flight(tp))) {              ca->last_ack = now_us;              ca->round_start = now_us;          } else if (before(now_us, ca->last_ack + 3000)) {              u32 base_owd = max(ca->delay_min / 2U, 125U);                ca->last_ack = now_us;              if (after(now_us, ca->round_start + base_owd)) {                  tp->snd_ssthresh = tp->snd_cwnd;                  return;              }          }      }        if (hystart_detect & HYSTART_DELAY) {          if (ca->sample_cnt < 8) {              ca->sample_cnt++;          } else {              s32 thresh = max(ca->delay_min + ca->delay_min / 8U,                       125U);                if (ca->rtt.min > thresh) {                  tp->snd_ssthresh = tp->snd_cwnd;              }          }      }  }    static s32 tcp_cdg_grad(struct cdg *ca)  {      s32 gmin = ca->rtt.min - ca->rtt_prev.min;      s32 gmax = ca->rtt.max - ca->rtt_prev.max;      s32 grad;        if (ca->gradients) {          ca->gsum.min += gmin - ca->gradients[ca->tail].min;          ca->gsum.max += gmax - ca->gradients[ca->tail].max;          ca->gradients[ca->tail].min = gmin;          ca->gradients[ca->tail].max = gmax;          ca->tail = (ca->tail + 1) & (window - 1);          gmin = ca->gsum.min;          gmax = ca->gsum.max;      }        /* We keep sums to ignore gradients during cwnd reductions;       * the paper's smoothed gradients otherwise simplify to:       * (rtt_latest - rtt_oldest) / window.       *       * We also drop division by window here.       */      grad = gmin > 0 ? gmin : gmax;        /* Extrapolate missing values in gradient window: */      if (!ca->gfilled) {          if (!ca->gradients && window > 1)              grad *= window; /* Memory allocation failed. */          else if (ca->tail == 0)              ca->gfilled = true;          else              grad = (grad * window) / (int)ca->tail;      }        /* Backoff was effectual: */      if (gmin <= -32 || gmax <= -32)          ca->backoff_cnt = 0;        if (use_tolerance) {          /* Reduce small variations to zero: */          gmin = DIV_ROUND_CLOSEST(gmin, 64);          gmax = DIV_ROUND_CLOSEST(gmax, 64);          if (gmin > 0 && gmax <= 0)              ca->state = CDG_FULL;          else if ((gmin > 0 && gmax > 0) || gmax < 0)              ca->state = CDG_NONFULL;      }      return grad;  }    void tcp_enter_cwr_1(struct sock *sk)  {      struct tcp_sock *tp = tcp_sk(sk);        tp->prior_ssthresh = 0;      if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {          tp->undo_marker = 0;          tp->high_seq = tp->snd_nxt;          tp->tlp_high_seq = 0;          tp->snd_cwnd_cnt = 0;          tp->prior_cwnd = tp->snd_cwnd;          tp->prr_delivered = 0;          tp->prr_out = 0;          tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);          if (tp->ecn_flags & TCP_ECN_OK)              tp->ecn_flags |= TCP_ECN_QUEUE_CWR;          tcp_set_ca_state(sk, TCP_CA_CWR);      }  }    static bool tcp_cdg_backoff(struct sock *sk, u32 grad)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);        if (prandom_u32() <= nexp_u32(grad * backoff_factor))          return false;        if (use_ineff) {          ca->backoff_cnt++;          if (ca->backoff_cnt > use_ineff)              return false;      }        ca->shadow_wnd = max(ca->shadow_wnd, tp->snd_cwnd);      ca->state = CDG_BACKOFF;      tcp_enter_cwr_1(sk);      return true;  }    void tcp_cong_avoid_ai_shadow(struct sock *sk, u32 w, u32 acked)  {      struct tcp_sock *tp = tcp_sk(sk);      struct cdg *ca = inet_csk_ca(sk);      if (ca->snd_cwnd_cnt >= w) {          ca->snd_cwnd_cnt = 0;          ca->shadow_wnd ++;      }        ca->snd_cwnd_cnt += acked;      if (ca->snd_cwnd_cnt >= w) {          u32 delta = ca->snd_cwnd_cnt / w;            ca->snd_cwnd_cnt -= delta * w;          ca->shadow_wnd += delta;      }      ca->shadow_wnd = min(ca->shadow_wnd, tp->snd_cwnd_clamp);  }    /* Not called in CWR or Recovery state. */  static void tcp_cdg_cong_avoid(struct sock *sk, u32 ack, u32 acked)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);      u32 prior_snd_cwnd;      u32 incr;        if (tp->snd_cwnd <= tp->snd_ssthresh && hystart_detect)          tcp_cdg_hystart_update(sk);        if (after(ack, ca->rtt_seq) && ca->rtt.v64) {          s32 grad = 0;            if (ca->rtt_prev.v64)              grad = tcp_cdg_grad(ca);          ca->rtt_seq = tp->snd_nxt;          ca->rtt_prev = ca->rtt;          ca->rtt.v64 = 0;          ca->last_ack = 0;          ca->sample_cnt = 0;            if (backoff && grad > 0 && tcp_cdg_backoff(sk, grad))              return;      }        if (!tcp_is_cwnd_limited(sk, tcp_packets_in_flight(tp))) {          ca->shadow_wnd = min(ca->shadow_wnd, tp->snd_cwnd);          return;      }        prior_snd_cwnd = tp->snd_cwnd;      tcp_reno_cong_avoid(sk, ack, acked);        incr = tp->snd_cwnd - prior_snd_cwnd;      ca->shadow_wnd = max(ca->shadow_wnd, ca->shadow_wnd + incr);  }    static void tcp_cdg_acked(struct sock *sk, u32 num_acked, s32 rtt_us)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);        if (rtt_us <= 0)          return;        /* A heuristic for filtering delayed ACKs, adapted from:       * D.A. Hayes. "Timing enhancements to the FreeBSD kernel to support       * delay and rate based TCP mechanisms." TR 100219A. CAIA, 2010.       */      if (tp->sacked_out == 0) {          if (num_acked == 1 && ca->delack) {              /* A delayed ACK is only used for the minimum if it is               * provenly lower than an existing non-zero minimum.               */              ca->rtt.min = min(ca->rtt.min, rtt_us);              ca->delack--;              return;          } else if (num_acked > 1 && ca->delack < 5) {              ca->delack++;          }      }        ca->rtt.min = min_not_zero(ca->rtt.min, rtt_us);      ca->rtt.max = max(ca->rtt.max, rtt_us);  }    static u32 tcp_cdg_ssthresh(struct sock *sk)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);        ca->undo_cwnd = tp->snd_cwnd;      ca->snd_cwnd_cnt = 0;      ca->ack_sack_cnt = tcp_packets_in_flight(tp);        if (ca->state == CDG_BACKOFF)          return max(2U, (tp->snd_cwnd * min(1024U, backoff_beta)) >> 10);        if (ca->state == CDG_NONFULL && use_tolerance)          return tp->snd_cwnd;        ca->shadow_wnd = max(min(ca->shadow_wnd >> 1, tp->snd_cwnd), 2U);      if (use_shadow)          return max3(2U, ca->shadow_wnd, tp->snd_cwnd >> 1);      return max(2U, tp->snd_cwnd >> 1);  }    static u32 tcp_cdg_undo_cwnd(struct sock *sk)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);      return max3(2U, ca->shadow_wnd, max(tp->snd_cwnd, ca->undo_cwnd));  }    static void tcp_cdg_cwnd_event(struct sock *sk, const enum tcp_ca_event ev)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);      struct cdg_minmax *gradients;    www.sratchina.com  易购娱乐 www.boyuanyl.cn      switch (ev) {      case CA_EVENT_CWND_RESTART:          gradients = ca->gradients;          if (gradients)              memset(gradients, 0, window * sizeof(gradients[0]));          memset(ca, 0, sizeof www.chuangshi88.cn(*ca));            ca->gradients = gradients;          ca->rtt_seq = tp->snd_nxt;          ca->shadow_wnd = tp->snd_cwnd;          break;      case CA_EVENT_COMPLETE_CWR:          ca->state = CDG_UNKNOWN;          ca->rtt_seq = tp->snd_nxt;          ca->rtt_prev = ca-www.sbsbo.cn>rtt;          ca->rtt.v64 =www.sbsbo.cc 0;          break;      default:          break;      }  }    static void tcp_cdg_init(struct www.linkenzc.cn sock *sk)  {      struct cdg *ca = www.linlenyl.cn inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);        /* We silently fall back to window = 1 if allocation fails. */      if (window > 1)          ca->gradients = kcalloc(window, sizeof(ca->gradients[0]),                      GFP_NOWAIT | __GFP_NOWARN);      ca->rtt_seq = tp->snd_nxt;      ca->shadow_wnd = tp->snd_cwnd;      ca->ack_sack_cnt = 0;  }    static void tcp_cdg_release(struct sock *sk)  {      struct cdg *ca = inet_csk_ca(sk);        kfree(ca->gradients);  }    static void cdg_main(struct sock *sk, struct rate_sample *rs)  {      struct inet_connection_sock *icsk = inet_csk(sk);      struct tcp_sock *tp = tcp_sk(sk);      struct cdg *ca = inet_csk_ca(sk);            if (!shadow_grow) {          rs->flag |= CDG_CONT;          return;      }                if (icsk->icsk_ca_state != TCP_CA_Open) {          if (rs->rtt_us) {              ca->rtt.min = min_not_zero(ca->rtt.min, (s32)rs->rtt_us);              ca->rtt.max = max(ca->rtt.max, (s32)rs->rtt_us);          }                    if (ca->state == CDG_NONFULL && use_tolerance) {               if (!shadow_fast && (ca->ack_sack_cnt < 0 || ca->ack_sack_cnt == 0) && ca->rtt.v64) {                  s32 grad = 0;                    if (ca->rtt_prev.v64)                      grad = tcp_cdg_grad(ca);                  ca->rtt_prev = ca->rtt;                  ca->ack_sack_cnt = tcp_packets_in_flight(tp);                  ca->rtt.v64 = 0;              }              ca->ack_sack_cnt -= rs->acked_sacked;              if (ca->state == CDG_NONFULL || shadow_fast) {                  tcp_cong_avoid_ai_shadow(sk, ca->shadow_wnd, rs->acked_sacked);                     tp->snd_cwnd = ca->shadow_wnd;              }                            rs->flag |= CDG_CONT;          }      } else {          rs->flag |= CDG_CONT;      }  }    static void cdg_state(struct sock *sk, u8 new_state)  {      struct cdg *ca = inet_csk_ca(sk);      struct tcp_sock *tp = tcp_sk(sk);        if (!recovery_restore)          return;      if (new_state == TCP_CA_Open)          tp->snd_cwnd = max(max(tp->snd_cwnd, ca->shadow_wnd), 2U);      if (new_state == TCP_CA_Loss) {          if (ca->state == CDG_NONFULL && use_tolerance) {              tp->snd_cwnd = ca->shadow_wnd;              if (loss_push)                  tcp_push_pending_frames(sk);          }       }  }    struct tcp_congestion_ops tcp_cdg __read_mostly = {      .cong_avoid = tcp_cdg_cong_avoid,      .cong_control   = cdg_main,      .set_state = cdg_state,      .cwnd_event = tcp_cdg_cwnd_event,      .pkts_acked = tcp_cdg_acked,      .undo_cwnd = tcp_cdg_undo_cwnd,      .ssthresh = tcp_cdg_ssthresh,      .release = tcp_cdg_release,      .init = tcp_cdg_init,      .owner = THIS_MODULE,      .name = "cdg",  };    static int __init tcp_cdg_register(void)  {      if (backoff_beta > 1024 || window < 1 || window > 256)          return -ERANGE;      if (!is_power_of_2(window))          return -EINVAL;        BUILD_BUG_ON(sizeof(struct cdg) > ICSK_CA_PRIV_SIZE);      tcp_register_congestion_control(&tcp_cdg);      return 0;  }    static void __exit tcp_cdg_unregister(void)  {      tcp_unregister_congestion_control(&tcp_cdg);  }    module_init(tcp_cdg_register);  module_exit(tcp_cdg_unregister);  MODULE_AUTHOR("...");  MODULE_LICENSE("GPL");  MODULE_DESCRIPTION("TCP CDG");