net/ipv4/Kconfig | 12 + net/ipv4/Makefile | 1 + net/ipv4/tcp_roccet.c | 686 ++++++++++++++++++++++++++++++++++++++++++ net/ipv4/tcp_roccet.h | 52 ++++ 4 files changed, 751 insertions(+) create mode 100644 net/ipv4/tcp_roccet.c create mode 100644 net/ipv4/tcp_roccet.h
TCP ROCCET is an extension of TCP CUBIC that improves its overall
performance. By its mode of function, CUBIC causes bufferbloat while
it tries to detect the available throughput of a network path. This is
particularly a problem with large buffers in mobile networks. A more
detailed description and analysis of this problem caused by TCP CUBIC
can be found in [1]. TCP ROCCET addresses this problem by adding two
additional metrics to detect congestion (queueing and bufferbloat)
on a network path. TCP ROCCET achieves better performance than CUBIC
and BBRv3, by maintaining similar throughput while reducing the latency.
In addition, TCP ROCCET does not have fairness issues when sharing a
link with TCP CUBIC and BBRv3. A paper that evaluates the performance
and function of TCP ROCCET has already been peer-reviewed and will be
presented at the WONS 2026 conference. A draft of this paper can be
found here [2].
[1] https://doi.org/10.1109/VTC2023-Fall60731.2023.10333357
[2] https://arxiv.org/abs/2510.25281
Signed-off-by: Lukas Prause <lukas.prause@ikt.uni-hannover.de>
Signed-off-by: Tim Fuechsel <t.fuechsel@gmx.de>
---
net/ipv4/Kconfig | 12 +
net/ipv4/Makefile | 1 +
net/ipv4/tcp_roccet.c | 686 ++++++++++++++++++++++++++++++++++++++++++
net/ipv4/tcp_roccet.h | 52 ++++
4 files changed, 751 insertions(+)
create mode 100644 net/ipv4/tcp_roccet.c
create mode 100644 net/ipv4/tcp_roccet.h
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index b71c22475c51..781a0db37309 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -664,6 +664,18 @@ config TCP_CONG_CDG
delay gradients." In Networking 2011. Preprint:
http://caia.swin.edu.au/cv/dahayes/content/networking2011-cdg-preprint.pdf
+config TCP_CONG_ROCCET
+ tristate "ROCCET TCP"
+ default n
+ help
+ TCP ROCCET is a sender-side only modification of the TCP CUBIC
+ protocol stack that optimizes the performance of TCP congestion
+ control. Especially for networks with large buffers (wireless,
+ cellular networks), TCP ROCCET has improved performance by maintaining
+ similar throughput as CUBIC while reducing the latency.
+ For more information, see: https://arxiv.org/abs/2510.25281
+
+
config TCP_CONG_BBR
tristate "BBR TCP"
default n
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index ec36d2ec059e..35fa62b6d07f 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -45,6 +45,7 @@ obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o
obj-$(CONFIG_INET_RAW_DIAG) += raw_diag.o
obj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o
+obj-$(CONFIG_TCP_CONG_ROCCET) += tcp_roccet.o
obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
obj-$(CONFIG_TCP_CONG_CDG) += tcp_cdg.o
obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o
diff --git a/net/ipv4/tcp_roccet.c b/net/ipv4/tcp_roccet.c
new file mode 100644
index 000000000000..998a97bcb03e
--- /dev/null
+++ b/net/ipv4/tcp_roccet.c
@@ -0,0 +1,686 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * TCP ROCCET: An RTT-Oriented CUBIC Congestion Control
+ * Extension for 5G and Beyond Networks
+ *
+ * TCP ROCCET is a new TCP congestion control
+ * algorithm suited for current cellular 5G NR beyond networks.
+ * It extends the kernel default congestion control CUBIC
+ * and improves its performance, and additionally solves an
+ * unwanted side effects of CUBIC’s implementation.
+ * ROCCET uses its own Slow Start, called LAUNCH, where loss
+ * is not considered as a congestion event.
+ * The congestion avoidance phase, called ORBITER, uses
+ * CUBIC's window growth function and adds, based on RTT
+ * and ACK rate, congestion events.
+ *
+ * A peer-reviewed paper on TCP ROCCET will be presented at the WONS 2026 conference.
+ * A draft of the paper is available here:
+ * https://arxiv.org/abs/2510.25281
+ *
+ *
+ * Further information about CUBIC:
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
+ * Home page:
+ * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
+ * This is from the implementation of CUBIC TCP in
+ * Sangtae Ha, Injong Rhee and Lisong Xu,
+ * "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
+ * in ACM SIGOPS Operating System Review, July 2008.
+ * Available from:
+ * http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
+ *
+ * CUBIC integrates a new slow start algorithm, called HyStart.
+ * The details of HyStart are presented in
+ * Sangtae Ha and Injong Rhee,
+ * "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
+ * Available from:
+ * http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
+ *
+ * All testing results are available from:
+ * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
+ *
+ * Unless CUBIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include "tcp_roccet.h"
+#include "linux/printk.h"
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+#include <linux/math64.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+/* Scale factor beta calculation (max_cwnd = snd_cwnd * beta) */
+#define BICTCP_BETA_SCALE 1024
+
+#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
+
+/* Alpha value for the sRrTT multiplied by 100.
+ * Here 20 represents a value of 0.2
+ */
+#define ROCCET_ALPHA_TIMES_100 20
+
+/* The amount of seconds ROCCET stores a minRTT.
+ * Enable "calculate_min_rtt" first.
+ */
+#define ROCCET_RTT_LOOKBACK_S 10
+
+/* Parameters that are specific to the ROCCET-Algorithm */
+static int sr_rtt_upper_bound __read_mostly = 100;
+static int ack_rate_diff_ss __read_mostly = 10;
+static int ack_rate_diff_ca __read_mostly = 200;
+static bool calculate_min_rtt __read_mostly;
+static bool ignore_loss __read_mostly;
+static int roccet_min_rtt_interpolation_factor __read_mostly = 70;
+
+module_param(sr_rtt_upper_bound, int, 0644);
+MODULE_PARM_DESC(sr_rtt_upper_bound, "ROCCET's upper bound for srRTT.");
+module_param(ack_rate_diff_ss, int, 0644);
+MODULE_PARM_DESC(ack_rate_diff_ss,
+ "ROCCET's threshold to exit slow start if ACK-rate defer by given amount of segments.");
+module_param(ack_rate_diff_ca, int, 0644);
+MODULE_PARM_DESC(ack_rate_diff_ca,
+ "ROCCET's threshold for ack-rate and cum_cwnd, in percentage of the current cwnd.");
+module_param(calculate_min_rtt, bool, 0644);
+MODULE_PARM_DESC(calculate_min_rtt,
+ "Calculate min RTT if no lower RTT occurs after 10 sec.");
+module_param(ignore_loss, bool, 0644);
+MODULE_PARM_DESC(ignore_loss, "Ignore loss as a congestion event.");
+module_param(roccet_min_rtt_interpolation_factor, int, 0644);
+MODULE_PARM_DESC(roccet_min_rtt_interpolation_factor,
+ "ROCCET factor for interpolating the current RTT with the last minRTT (minRTT = (factor * currRTT + (100-factor) * minRTT) / 100)");
+
+static bool fast_convergence __read_mostly = true;
+static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
+static int initial_ssthresh __read_mostly;
+static int bic_scale __read_mostly = 41;
+static bool tcp_friendliness __read_mostly = true;
+
+static u32 cube_rtt_scale __read_mostly;
+static u32 beta_scale __read_mostly;
+static u64 cube_factor __read_mostly;
+
+/* Note parameters that are used for precomputing scale factors are read-only */
+module_param(fast_convergence, bool, 0644);
+MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
+module_param(beta, int, 0644);
+MODULE_PARM_DESC(beta, "beta for multiplicative increase");
+module_param(initial_ssthresh, int, 0644);
+MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
+module_param(bic_scale, int, 0444);
+MODULE_PARM_DESC(bic_scale,
+ "scale (scaled by 1024) value for bic function (bic_scale/1024)");
+module_param(tcp_friendliness, bool, 0644);
+MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
+
+static inline void roccettcp_reset(struct roccettcp *ca)
+{
+ memset(ca, 0, offsetof(struct roccettcp, curr_rtt));
+ ca->bw_limit.sum_cwnd = 1;
+ ca->bw_limit.sum_acked = 1;
+ ca->bw_limit.next_check = 0;
+ ca->curr_min_rtt_timed.rtt = ~0U;
+ ca->curr_min_rtt_timed.time = ~0U;
+ ca->ece_srrtt = 0;
+ ca->ece_cwnd = 2;
+}
+
+static inline void update_min_rtt(struct sock *sk)
+{
+ struct roccettcp *ca = inet_csk_ca(sk);
+ u32 now = jiffies_to_usecs(tcp_jiffies32);
+
+ if (now - ca->curr_min_rtt_timed.time >
+ ROCCET_RTT_LOOKBACK_S * USEC_PER_SEC &&
+ calculate_min_rtt) {
+ u32 new_min_rtt = max(ca->curr_rtt, 1);
+ u32 old_min_rtt = ca->curr_min_rtt_timed.rtt;
+
+ u32 interpolated_min_rtt =
+ (new_min_rtt * roccet_min_rtt_interpolation_factor +
+ old_min_rtt *
+ (100 - roccet_min_rtt_interpolation_factor)) /
+ 100;
+
+ ca->curr_min_rtt_timed.rtt = interpolated_min_rtt;
+ ca->curr_min_rtt_timed.time = now;
+ }
+
+ /* Check if new lower min RTT was found. If so, set it directly */
+ if (ca->curr_rtt < ca->curr_min_rtt_timed.rtt) {
+ ca->curr_min_rtt_timed.rtt = max(ca->curr_rtt, 1);
+ ca->curr_min_rtt_timed.time = now;
+ }
+}
+
+/* Return difference between last and current ack rate.
+ */
+static inline int get_ack_rate_diff(struct roccettcp *ca)
+{
+ return ca->ack_rate.last_rate - ca->ack_rate.curr_rate;
+}
+
+/* Update ack rate sampled by 100ms.
+ */
+static inline void update_ack_rate(struct sock *sk)
+{
+ struct roccettcp *ca = inet_csk_ca(sk);
+ u32 now = jiffies_to_usecs(tcp_jiffies32);
+ u32 interval = USEC_PER_MSEC * 100;
+
+ if ((u32)(now - ca->ack_rate.last_rate_time) >= interval) {
+ ca->ack_rate.last_rate_time = now;
+ ca->ack_rate.last_rate = ca->ack_rate.curr_rate;
+ ca->ack_rate.curr_rate = ca->ack_rate.cnt;
+ ca->ack_rate.cnt = 0;
+ } else {
+ ca->ack_rate.cnt += 1;
+ }
+}
+
+/* Compute srRTT.
+ */
+static inline void update_srrtt(struct sock *sk)
+{
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ if (ca->curr_min_rtt_timed.rtt == 0)
+ return;
+
+ /* Calculate the new rRTT (Scaled by 100).
+ * 100 * ((sRTT - sRTT_min) / sRTT_min)
+ */
+ u32 rrtt = (100 * (ca->curr_rtt - ca->curr_min_rtt_timed.rtt)) /
+ ca->curr_min_rtt_timed.rtt;
+
+ // (1 - alpha) * srRTT + alpha * rRTT
+ ca->curr_srrtt = ((100 - ROCCET_ALPHA_TIMES_100) * ca->curr_srrtt +
+ ROCCET_ALPHA_TIMES_100 * rrtt) /
+ 100;
+}
+
+__bpf_kfunc static void roccettcp_init(struct sock *sk)
+{
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ roccettcp_reset(ca);
+
+ if (initial_ssthresh)
+ tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
+
+ /* Initial roccet parameters */
+ ca->roccet_last_event_time_us = 0;
+ ca->ack_rate.last_rate = 0;
+ ca->ack_rate.last_rate_time = 0;
+ ca->ack_rate.curr_rate = 0;
+ ca->ack_rate.cnt = 0;
+}
+
+__bpf_kfunc static void roccettcp_cwnd_event(struct sock *sk,
+ enum tcp_ca_event event)
+{
+ if (event == CA_EVENT_TX_START) {
+ struct roccettcp *ca = inet_csk_ca(sk);
+ u32 now = tcp_jiffies32;
+ s32 delta;
+
+ delta = now - tcp_sk(sk)->lsndtime;
+
+ /* We were application limited (idle) for a while.
+ * Shift epoch_start to keep cwnd growth to cubic curve.
+ */
+ if (ca->epoch_start && delta > 0) {
+ ca->epoch_start += delta;
+ if (after(ca->epoch_start, now))
+ ca->epoch_start = now;
+ }
+ return;
+ }
+}
+
+/* calculate the cubic root of x using a table lookup followed by one
+ * Newton-Raphson iteration.
+ * Avg err ~= 0.195%
+ */
+static u32 cubic_root(u64 a)
+{
+ u32 x, b, shift;
+ /* cbrt(x) MSB values for x MSB values in [0..63].
+ * Precomputed then refined by hand - Willy Tarreau
+ *
+ * For x in [0..63],
+ * v = cbrt(x << 18) - 1
+ * cbrt(x) = (v[x] + 10) >> 6
+ */
+ static const u8 v[] = {
+ /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
+ /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
+ /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
+ /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
+ /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
+ /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
+ /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
+ /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
+ };
+
+ b = fls64(a);
+ if (b < 7) {
+ /* a in [0..63] */
+ return ((u32)v[(u32)a] + 35) >> 6;
+ }
+
+ b = ((b * 84) >> 8) - 1;
+ shift = (a >> (b * 3));
+
+ x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
+
+ /* Newton-Raphson iteration
+ * 2
+ * x = ( 2 * x + a / x ) / 3
+ * k+1 k k
+ */
+ x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
+ x = ((x * 341) >> 10);
+ return x;
+}
+
+/* Compute congestion window to use.
+ */
+static inline void bictcp_update(struct roccettcp *ca, u32 cwnd, u32 acked)
+{
+ u32 delta, bic_target, max_cnt;
+ u64 offs, t;
+
+ ca->ack_cnt += acked; /* count the number of ACKed packets */
+
+ if (ca->last_cwnd == cwnd &&
+ (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
+ return;
+
+ /* The CUBIC function can update ca->cnt at most once per jiffy.
+ * On all cwnd reduction events, ca->epoch_start is set to 0,
+ * which will force a recalculation of ca->cnt.
+ */
+ if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
+ goto tcp_friendliness;
+
+ ca->last_cwnd = cwnd;
+ ca->last_time = tcp_jiffies32;
+
+ if (ca->epoch_start == 0) {
+ ca->epoch_start = tcp_jiffies32; /* record beginning */
+ ca->ack_cnt = acked; /* start counting */
+ ca->tcp_cwnd = cwnd; /* syn with cubic */
+
+ if (ca->last_max_cwnd <= cwnd) {
+ ca->bic_K = 0;
+ ca->bic_origin_point = cwnd;
+ } else {
+ /* Compute new K based on
+ * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
+ */
+ ca->bic_K = cubic_root(cube_factor *
+ (ca->last_max_cwnd - cwnd));
+ ca->bic_origin_point = ca->last_max_cwnd;
+ }
+ }
+
+ /* cubic function - calc */
+ /* calculate c * time^3 / rtt,
+ * while considering overflow in calculation of time^3
+ * (so time^3 is done by using 64 bit)
+ * and without the support of division of 64bit numbers
+ * (so all divisions are done by using 32 bit)
+ * also NOTE the unit of those variables
+ * time = (t - K) / 2^bictcp_HZ
+ * c = bic_scale >> 10
+ * rtt = (srtt >> 3) / HZ
+ * !!! The following code does not have overflow problems,
+ * if the cwnd < 1 million packets !!!
+ */
+
+ t = (s32)(tcp_jiffies32 - ca->epoch_start);
+ t += usecs_to_jiffies(ca->delay_min);
+
+ /* change the unit from HZ to bictcp_HZ */
+ t <<= BICTCP_HZ;
+ do_div(t, HZ);
+
+ if (t < ca->bic_K) /* t - K */
+ offs = ca->bic_K - t;
+ else
+ offs = t - ca->bic_K;
+
+ /* c/rtt * (t-K)^3 */
+ delta = (cube_rtt_scale * offs * offs * offs) >> (10 + 3 * BICTCP_HZ);
+ if (t < ca->bic_K) /* below origin*/
+ bic_target = ca->bic_origin_point - delta;
+ else /* above origin*/
+ bic_target = ca->bic_origin_point + delta;
+
+ /* cubic function - calc bictcp_cnt*/
+ if (bic_target > cwnd)
+ ca->cnt = cwnd / (bic_target - cwnd);
+ else
+ ca->cnt = 100 * cwnd; /* very small increment*/
+
+ /* The initial growth of cubic function may be too conservative
+ * when the available bandwidth is still unknown.
+ */
+ if (ca->last_max_cwnd == 0 && ca->cnt > 20)
+ ca->cnt = 20; /* increase cwnd 5% per RTT */
+
+tcp_friendliness:
+ /* TCP Friendly */
+ if (tcp_friendliness) {
+ u32 scale = beta_scale;
+
+ delta = (cwnd * scale) >> 3;
+ while (ca->ack_cnt > delta) { /* update tcp cwnd */
+ ca->ack_cnt -= delta;
+ ca->tcp_cwnd++;
+ }
+
+ if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
+ delta = ca->tcp_cwnd - cwnd;
+ max_cnt = cwnd / delta;
+ if (ca->cnt > max_cnt)
+ ca->cnt = max_cnt;
+ }
+ }
+
+ /* The maximum rate of cwnd increase CUBIC allows is 1 packet per
+ * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
+ */
+ ca->cnt = max(ca->cnt, 2U);
+}
+
+__bpf_kfunc static void roccettcp_cong_avoid(struct sock *sk, u32 ack,
+ u32 acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ u32 now = jiffies_to_usecs(tcp_jiffies32);
+ u32 bw_limit_detect = 0;
+ u32 roccet_xj;
+ u32 jitter;
+
+ if (ca->last_rtt > ca->curr_rtt)
+ jitter = ca->last_rtt - ca->curr_rtt;
+ else
+ jitter = ca->curr_rtt - ca->last_rtt;
+
+ /* Update roccet parameters */
+ update_ack_rate(sk);
+ update_min_rtt(sk);
+ update_srrtt(sk);
+
+ /* Reset ECE handling if we already have more bandwidth
+ * than we received the last ECE.
+ */
+ if (ca->ece_srrtt > 0) {
+ if (tcp_snd_cwnd(tp) >= ca->ece_cwnd)
+ ca->ece_srrtt = 0;
+ }
+
+ /* ROCCET drain.
+ * Do not increase the cwnd for 100ms after a roccet congestion event
+ */
+ if (now - ca->roccet_last_event_time_us <= 100 * USEC_PER_MSEC)
+ return;
+
+ /* LAUNCH: Detect an exit point for tcp slow start
+ * in networks with large buffers of multiple BDP
+ * Like in cellular networks (5G, ...).
+ * Or exit LAUNCH if cwnd is too large for application layer
+ * data rate.
+ */
+
+ if ((tcp_in_slow_start(tp) && ca->curr_srrtt > sr_rtt_upper_bound &&
+ get_ack_rate_diff(ca) >= ack_rate_diff_ss) ||
+ (!tcp_is_cwnd_limited(sk) && tcp_in_slow_start(tp))) {
+ ca->epoch_start = 0;
+
+ /* Handle initial slow start. Here we observe the most problems */
+ if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) {
+ tcp_sk(sk)->snd_ssthresh = tcp_snd_cwnd(tp) / 2;
+ tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) / 2);
+ } else {
+ tcp_sk(sk)->snd_ssthresh =
+ tcp_snd_cwnd(tp) - (tcp_snd_cwnd(tp) / 3);
+ tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) -
+ (tcp_snd_cwnd(tp) / 3));
+ }
+ ca->roccet_last_event_time_us = now;
+ return;
+ }
+
+ if (tcp_in_slow_start(tp)) {
+ acked = tcp_slow_start(tp, acked);
+ if (!acked)
+ return;
+ }
+
+ if (ca->bw_limit.next_check == 0)
+ ca->bw_limit.next_check = now + 5 * ca->curr_rtt;
+
+ ca->bw_limit.sum_cwnd += tcp_snd_cwnd(tp);
+ ca->bw_limit.sum_acked += acked;
+
+ if (ca->bw_limit.next_check < now) {
+ /* We send more data as we got acked in the last 5 RTTs */
+ if ((ca->bw_limit.sum_cwnd * 100) / ca->bw_limit.sum_acked >=
+ ack_rate_diff_ca)
+ bw_limit_detect = 1;
+
+ /* reset struct and set next end of period */
+ ca->bw_limit.sum_cwnd = 1;
+
+ /* set to 1 to avoid division by zero */
+ ca->bw_limit.sum_acked = 1;
+ ca->bw_limit.next_check = now + 5 * ca->curr_rtt;
+ }
+
+ /* Respects the jitter of the connection and add it on top of the upper bound
+ * for the srRTT
+ */
+ roccet_xj = ((jitter * 100) / ca->curr_min_rtt_timed.rtt) +
+ sr_rtt_upper_bound;
+ if (roccet_xj < sr_rtt_upper_bound)
+ roccet_xj = sr_rtt_upper_bound;
+
+ /* This is true if we recently received an ECE bit.
+ * Therefore we should respect the srRTT at this point.
+ */
+ if (ca->ece_srrtt < roccet_xj && ca->ece_srrtt > 0)
+ roccet_xj = ca->ece_srrtt;
+
+ if (ca->curr_srrtt > roccet_xj && (bw_limit_detect || ca->ece_srrtt > 0)) {
+ ca->epoch_start = 0;
+ ca->roccet_last_event_time_us = now;
+ ca->cnt = 100 * tcp_snd_cwnd(tp);
+
+ /* Set Wmax if cwnd is larger than the old Wmax */
+ if (tcp_snd_cwnd(tp) > ca->last_max_cwnd)
+ ca->last_max_cwnd = tcp_snd_cwnd(tp);
+
+ tcp_snd_cwnd_set(tp, min(tp->snd_cwnd_clamp,
+ max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U)));
+ tp->snd_ssthresh = tcp_snd_cwnd(tp);
+ return;
+ }
+
+ /* Terminates this function if cwnd is not fully utilized.
+ * In mobile networks like 5G, this termination causes the cwnd to be frozen at
+ * an excessively high value. This is because slow start or HyStart massively
+ * exceed the available bandwidth and leave the cwnd at an excessively high
+ * value. The cwnd cannot therefore be fully utilized because it is limited by
+ * the connection capacity.
+ */
+ if (!tcp_is_cwnd_limited(sk))
+ return;
+
+ bictcp_update(ca, tcp_snd_cwnd(tp), acked);
+ tcp_cong_avoid_ai(tp, max(1, ca->cnt), acked);
+}
+
+__bpf_kfunc static u32 roccettcp_recalc_ssthresh(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ if (ignore_loss)
+ return tcp_snd_cwnd(tp);
+
+ /* Don't exit slow start if loss occurs. */
+ if (tcp_in_slow_start(tp))
+ return tcp_snd_cwnd(tp);
+
+ ca->epoch_start = 0; /* end of epoch */
+
+ /* Wmax and fast convergence */
+ if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
+ ca->last_max_cwnd =
+ (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta)) /
+ (2 * BICTCP_BETA_SCALE);
+ else
+ ca->last_max_cwnd = tcp_snd_cwnd(tp);
+
+ return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+__bpf_kfunc static void roccettcp_state(struct sock *sk, u8 new_state)
+{
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ if (new_state == TCP_CA_Loss)
+ roccettcp_reset(ca);
+}
+
+__bpf_kfunc static void roccettcp_acked(struct sock *sk,
+ const struct ack_sample *sample)
+{
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ /* Some calls are for duplicates without timestamps */
+ if (sample->rtt_us < 0)
+ return;
+
+ /* Discard delay samples right after fast recovery */
+ if (ca->epoch_start && (s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
+ return;
+
+ u32 delay = sample->rtt_us;
+
+ if (delay == 0)
+ delay = 1;
+
+ /* first time call or link delay decreases */
+ if (ca->delay_min == 0 || ca->delay_min > delay)
+ ca->delay_min = delay;
+
+ /* Get valid sample for roccet */
+ if (sample->rtt_us > 0) {
+ ca->last_rtt = ca->curr_rtt;
+ ca->curr_rtt = sample->rtt_us;
+ }
+}
+
+__bpf_kfunc static void roccet_in_ack_event(struct sock *sk, u32 flags)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct roccettcp *ca = inet_csk_ca(sk);
+
+ /* Handle ECE bit.
+ * Processing of ECE events is done in roccettcp_cong_avoid()
+ */
+ if (flags & CA_ACK_ECE) {
+ ca->ece_srrtt = ca->curr_srrtt;
+ ca->ece_cwnd = tcp_snd_cwnd(tp);
+ }
+}
+
+static struct tcp_congestion_ops roccet_tcp __read_mostly = {
+ .init = roccettcp_init,
+ .ssthresh = roccettcp_recalc_ssthresh,
+ .cong_avoid = roccettcp_cong_avoid,
+ .set_state = roccettcp_state,
+ .undo_cwnd = tcp_reno_undo_cwnd,
+ .cwnd_event = roccettcp_cwnd_event,
+ .pkts_acked = roccettcp_acked,
+ .in_ack_event = roccet_in_ack_event,
+ .owner = THIS_MODULE,
+ .name = "roccet",
+};
+
+BTF_KFUNCS_START(tcp_roccet_check_kfunc_ids)
+BTF_ID_FLAGS(func, roccettcp_init)
+BTF_ID_FLAGS(func, roccettcp_recalc_ssthresh)
+BTF_ID_FLAGS(func, roccettcp_cong_avoid)
+BTF_ID_FLAGS(func, roccettcp_state)
+BTF_ID_FLAGS(func, roccettcp_cwnd_event)
+BTF_ID_FLAGS(func, roccettcp_acked)
+BTF_KFUNCS_END(tcp_roccet_check_kfunc_ids)
+
+static const struct btf_kfunc_id_set tcp_roccet_kfunc_set = {
+ .owner = THIS_MODULE,
+ .set = &tcp_roccet_check_kfunc_ids,
+};
+
+static int __init roccettcp_register(void)
+{
+ int ret;
+
+ BUILD_BUG_ON(sizeof(struct roccettcp) > ICSK_CA_PRIV_SIZE);
+
+ /* Precompute a bunch of the scaling factors that are used per-packet
+ * based on SRTT of 100ms
+ */
+
+ beta_scale =
+ 8 * (BICTCP_BETA_SCALE + beta) / 3 / (BICTCP_BETA_SCALE - beta);
+
+ cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
+
+ /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
+ * so K = cubic_root( (wmax-cwnd)*rtt/c )
+ * the unit of K is bictcp_HZ=2^10, not HZ
+ *
+ * c = bic_scale >> 10
+ * rtt = 100ms
+ *
+ * the following code has been designed and tested for
+ * cwnd < 1 million packets
+ * RTT < 100 seconds
+ * HZ < 1,000,00 (corresponding to 10 nano-second)
+ */
+
+ /* 1/c * 2^2*bictcp_HZ * srtt */
+ cube_factor = 1ull << (10 + 3 * BICTCP_HZ); /* 2^40 */
+
+ /* divide by bic_scale and by constant Srtt (100ms) */
+ do_div(cube_factor, bic_scale * 10);
+
+ ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+ &tcp_roccet_kfunc_set);
+ if (ret < 0)
+ return ret;
+ return tcp_register_congestion_control(&roccet_tcp);
+}
+
+static void __exit roccettcp_unregister(void)
+{
+ tcp_unregister_congestion_control(&roccet_tcp);
+}
+
+module_init(roccettcp_register);
+module_exit(roccettcp_unregister);
+
+MODULE_AUTHOR("Lukas Prause, Tim Fuechsel");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ROCCET TCP");
+MODULE_VERSION("1.0");
diff --git a/net/ipv4/tcp_roccet.h b/net/ipv4/tcp_roccet.h
new file mode 100644
index 000000000000..5168d57efec5
--- /dev/null
+++ b/net/ipv4/tcp_roccet.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * TCP ROCCET congestion control interface
+ */
+#ifndef __TCP_ROCCET_H
+#define __TCP_ROCCET_H 1
+
+#include <linux/math64.h>
+
+struct ack_rate {
+ u16 last_rate; /* Last ACK-rate */
+ u32 last_rate_time; /* Timestamp of the last ACK-rate */
+ u16 curr_rate; /* Current ACK-rate */
+ u16 cnt; /* Used for counting acks */
+};
+
+struct bandwidth_limit_detected {
+ u32 sum_cwnd; /* sum of cwnd during time interval */
+ u32 sum_acked; /* sum of received acks during time interval */
+ u32 next_check; /* end/upper bound of time interval */
+};
+
+struct timed_rtt {
+ u32 time; /* Time of recoding */
+ u32 rtt; /* Measured RTT */
+};
+
+/* Based on the BICTCP struct with additions specific for the ROCCET-Algorithm */
+struct roccettcp {
+ u32 cnt; /* increase cwnd by 1 after ACKs */
+ u32 last_max_cwnd; /* last maximum snd_cwnd */
+ u32 last_cwnd; /* last snd_cwnd */
+ u32 last_time; /* time when updated last_cwnd */
+ u32 bic_origin_point; /* origin point of bic function */
+ u32 bic_K; /* time to origin point from the beginning of the current epoch */
+ u32 delay_min; /* min delay (usec) */
+ u32 epoch_start; /* beginning of an epoch */
+ u32 ack_cnt; /* number of acks */
+ u32 tcp_cwnd; /* estimated tcp cwnd */
+ u32 curr_rtt; /* minimum rtt of current round */
+
+ u32 roccet_last_event_time_us; /* last time ROCCET was triggered */
+ u32 ece_cwnd; /* cwnd when a ECE bit was received */
+ u32 ece_srrtt; /* srRTT when the ECE was received */
+ struct timed_rtt curr_min_rtt_timed; /* observed minRTT with the timestamp */
+ u32 curr_srrtt; /* srRTT calculated based on the latest ACK */
+ struct ack_rate ack_rate; /* last and the current ACK rate */
+ struct bandwidth_limit_detected bw_limit;
+ u32 last_rtt; /* Used for jitter calculation */
+};
+
+#endif /* __TCP_ROCCET_H */
--
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