我对TCP CDG拥塞控制算法的改进和优化
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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");
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