From nobody Sat Feb 7 06:13:45 2026 Received: from mout.gmx.net (mout.gmx.net [212.227.15.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 984773A9014; Thu, 5 Feb 2026 13:23:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=212.227.15.15 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770297813; cv=none; b=a9AeHfUXzm+vABxsT0j7y7SqgZGLq2LeDCDRXQLZmNTwZUVZ751fcbpdsstfJxN1/WYjJwot/eUVSn5HSZKGQH/T53XCw8pzhn0jE5JsPn18LOWFsAam4fNz11ur5M0cOZh3VJU4PuU262z+siJpgJoYmtCqryAyTney1JlShxg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770297813; c=relaxed/simple; bh=K7d+SwqplWG5ChgdhsdBYH6Y5QiqS0/9Pm9ni6YWJ04=; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=PlMx2kQvvIGBCJUNOJ4CiON52F+udoiMnuSOb+qYSoDkbF7lyWcSGeo/lPnYAbtUWx8hzBUNijllEgWwCmoWbJ3rEQAPKCGBqNxP1jF/jI/wJ3I13xp3F03LGxLJ3RduZWQz4OSpqDJ5xnpPsXr+zTNGahy6EAL45oFk2OvxUpw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=gmx.de; spf=pass smtp.mailfrom=gmx.de; dkim=pass (2048-bit key) header.d=gmx.de header.i=t.fuechsel@gmx.de header.b=BsUtiZre; arc=none smtp.client-ip=212.227.15.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=gmx.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmx.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmx.de header.i=t.fuechsel@gmx.de header.b="BsUtiZre" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmx.de; s=s31663417; t=1770297809; x=1770902609; i=t.fuechsel@gmx.de; bh=fkY8rvnvbfWaCE9XczzStxU9xymITjm581g3RP/NSgg=; h=X-UI-Sender-Class:Date:From:To:Subject:Message-ID:MIME-Version: Content-Type:Content-Transfer-Encoding:cc: content-transfer-encoding:content-type:date:from:message-id: mime-version:reply-to:subject:to; b=BsUtiZrefUbJkwMTQ00I7fMl3Vum2CnuRJaUlGQSc14WvCeafO6fLP/3DVwVekhZ 9wBfwi1QZEuNxTWVpNsBabIrcatsp+EUM+a+8O2s1cSWAf+A+nr0rKGuxTush65Ga 83ZyD5v3+nPcG9yOkEeJkeaoH58f7Vi/U7P8oInwIw+o5zfwf5CFwQvIdkmRUzXQZ LM7DwivCs6rA8ZnY8aq72xTSqL/pyvjo1xeiydpGivFN6YpOIPeO6/iUnsVXw8tFF Q0o6MFIasrWY6FfLNnzKvxtsvgJvkTfefP7q+wq4cMi0yWguIxzYPlT8KGC4aABcw 6y8GgVhq4So78CqLuQ== X-UI-Sender-Class: 724b4f7f-cbec-4199-ad4e-598c01a50d3a Received: from volt-roccet-vm ([130.75.172.138]) by mail.gmx.net (mrgmx005 [212.227.17.184]) with ESMTPSA (Nemesis) id 1N3siA-1vf9aj1BmS-00tJUX; Thu, 05 Feb 2026 14:23:29 +0100 Date: Thu, 5 Feb 2026 14:23:26 +0100 From: Tim Fuechsel To: "David S. Miller" , David Ahern , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, lukas.prause@ikt.uni-hannover.de, t.fuechsel@gmx.de Subject: [RFC] tcp: Add TCP ROCCET congestion control module. 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6zcFolEKeMypMG2DNNnqcOdUEmJYDB3B9RDWYR4xLibambbI2e2qwklCA1YSPPVQgsU53M0FI yft9j+ZsMyNgbmHTOTbbSXYgLvLbg Content-Type: text/plain; charset="utf-8" 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 Signed-off-by: Tim Fuechsel --- 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-preprin= t.pdf =20 +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 maintaini= ng + 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-$(CONFIG_INET_TCP_DIAG) +=3D tcp_diag.o obj-$(CONFIG_INET_UDP_DIAG) +=3D udp_diag.o obj-$(CONFIG_INET_RAW_DIAG) +=3D raw_diag.o obj-$(CONFIG_TCP_CONG_BBR) +=3D tcp_bbr.o +obj-$(CONFIG_TCP_CONG_ROCCET) +=3D tcp_roccet.o obj-$(CONFIG_TCP_CONG_BIC) +=3D tcp_bic.o obj-$(CONFIG_TCP_CONG_CDG) +=3D tcp_cdg.o obj-$(CONFIG_TCP_CONG_CUBIC) +=3D 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=E2=80=99s 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 +#include +#include +#include +#include +#include + +/* Scale factor beta calculation (max_cwnd =3D snd_cwnd * beta) */ +#define BICTCP_BETA_SCALE 1024 + +#define BICTCP_HZ 10 /* BIC HZ 2^10 =3D 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 =3D 100; +static int ack_rate_diff_ss __read_mostly =3D 10; +static int ack_rate_diff_ca __read_mostly =3D 200; +static bool calculate_min_rtt __read_mostly; +static bool ignore_loss __read_mostly; +static int roccet_min_rtt_interpolation_factor __read_mostly =3D 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 amoun= t 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 cur= rent 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 =3D (factor * currRTT + (100-factor) * minRTT) / 100)"); + +static bool fast_convergence __read_mostly =3D true; +static int beta __read_mostly =3D 717; /* =3D 717/1024 (BICTCP_BETA_SCALE)= */ +static int initial_ssthresh __read_mostly; +static int bic_scale __read_mostly =3D 41; +static bool tcp_friendliness __read_mostly =3D 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-o= nly */ +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 =3D 1; + ca->bw_limit.sum_acked =3D 1; + ca->bw_limit.next_check =3D 0; + ca->curr_min_rtt_timed.rtt =3D ~0U; + ca->curr_min_rtt_timed.time =3D ~0U; + ca->ece_srrtt =3D 0; + ca->ece_cwnd =3D 2; +} + +static inline void update_min_rtt(struct sock *sk) +{ + struct roccettcp *ca =3D inet_csk_ca(sk); + u32 now =3D 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 =3D max(ca->curr_rtt, 1); + u32 old_min_rtt =3D ca->curr_min_rtt_timed.rtt; + + u32 interpolated_min_rtt =3D + (new_min_rtt * roccet_min_rtt_interpolation_factor + + old_min_rtt * + (100 - roccet_min_rtt_interpolation_factor)) / + 100; + + ca->curr_min_rtt_timed.rtt =3D interpolated_min_rtt; + ca->curr_min_rtt_timed.time =3D 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 =3D max(ca->curr_rtt, 1); + ca->curr_min_rtt_timed.time =3D 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 =3D inet_csk_ca(sk); + u32 now =3D jiffies_to_usecs(tcp_jiffies32); + u32 interval =3D USEC_PER_MSEC * 100; + + if ((u32)(now - ca->ack_rate.last_rate_time) >=3D interval) { + ca->ack_rate.last_rate_time =3D now; + ca->ack_rate.last_rate =3D ca->ack_rate.curr_rate; + ca->ack_rate.curr_rate =3D ca->ack_rate.cnt; + ca->ack_rate.cnt =3D 0; + } else { + ca->ack_rate.cnt +=3D 1; + } +} + +/* Compute srRTT. + */ +static inline void update_srrtt(struct sock *sk) +{ + struct roccettcp *ca =3D inet_csk_ca(sk); + + if (ca->curr_min_rtt_timed.rtt =3D=3D 0) + return; + + /* Calculate the new rRTT (Scaled by 100). + * 100 * ((sRTT - sRTT_min) / sRTT_min) + */ + u32 rrtt =3D (100 * (ca->curr_rtt - ca->curr_min_rtt_timed.rtt)) / + ca->curr_min_rtt_timed.rtt; + + // (1 - alpha) * srRTT + alpha * rRTT + ca->curr_srrtt =3D ((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 =3D inet_csk_ca(sk); + + roccettcp_reset(ca); + + if (initial_ssthresh) + tcp_sk(sk)->snd_ssthresh =3D initial_ssthresh; + + /* Initial roccet parameters */ + ca->roccet_last_event_time_us =3D 0; + ca->ack_rate.last_rate =3D 0; + ca->ack_rate.last_rate_time =3D 0; + ca->ack_rate.curr_rate =3D 0; + ca->ack_rate.cnt =3D 0; +} + +__bpf_kfunc static void roccettcp_cwnd_event(struct sock *sk, + enum tcp_ca_event event) +{ + if (event =3D=3D CA_EVENT_TX_START) { + struct roccettcp *ca =3D inet_csk_ca(sk); + u32 now =3D tcp_jiffies32; + s32 delta; + + delta =3D 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 +=3D delta; + if (after(ca->epoch_start, now)) + ca->epoch_start =3D now; + } + return; + } +} + +/* calculate the cubic root of x using a table lookup followed by one + * Newton-Raphson iteration. + * Avg err ~=3D 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 =3D cbrt(x << 18) - 1 + * cbrt(x) =3D (v[x] + 10) >> 6 + */ + static const u8 v[] =3D { + /* 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 =3D fls64(a); + if (b < 7) { + /* a in [0..63] */ + return ((u32)v[(u32)a] + 35) >> 6; + } + + b =3D ((b * 84) >> 8) - 1; + shift =3D (a >> (b * 3)); + + x =3D ((u32)(((u32)v[shift] + 10) << b)) >> 6; + + /* Newton-Raphson iteration + * 2 + * x =3D ( 2 * x + a / x ) / 3 + * k+1 k k + */ + x =3D (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); + x =3D ((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 +=3D acked; /* count the number of ACKed packets */ + + if (ca->last_cwnd =3D=3D cwnd && + (s32)(tcp_jiffies32 - ca->last_time) <=3D 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 =3D=3D ca->last_time) + goto tcp_friendliness; + + ca->last_cwnd =3D cwnd; + ca->last_time =3D tcp_jiffies32; + + if (ca->epoch_start =3D=3D 0) { + ca->epoch_start =3D tcp_jiffies32; /* record beginning */ + ca->ack_cnt =3D acked; /* start counting */ + ca->tcp_cwnd =3D cwnd; /* syn with cubic */ + + if (ca->last_max_cwnd <=3D cwnd) { + ca->bic_K =3D 0; + ca->bic_origin_point =3D cwnd; + } else { + /* Compute new K based on + * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) + */ + ca->bic_K =3D cubic_root(cube_factor * + (ca->last_max_cwnd - cwnd)); + ca->bic_origin_point =3D 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 =3D (t - K) / 2^bictcp_HZ + * c =3D bic_scale >> 10 + * rtt =3D (srtt >> 3) / HZ + * !!! The following code does not have overflow problems, + * if the cwnd < 1 million packets !!! + */ + + t =3D (s32)(tcp_jiffies32 - ca->epoch_start); + t +=3D usecs_to_jiffies(ca->delay_min); + + /* change the unit from HZ to bictcp_HZ */ + t <<=3D BICTCP_HZ; + do_div(t, HZ); + + if (t < ca->bic_K) /* t - K */ + offs =3D ca->bic_K - t; + else + offs =3D t - ca->bic_K; + + /* c/rtt * (t-K)^3 */ + delta =3D (cube_rtt_scale * offs * offs * offs) >> (10 + 3 * BICTCP_HZ); + if (t < ca->bic_K) /* below origin*/ + bic_target =3D ca->bic_origin_point - delta; + else /* above origin*/ + bic_target =3D ca->bic_origin_point + delta; + + /* cubic function - calc bictcp_cnt*/ + if (bic_target > cwnd) + ca->cnt =3D cwnd / (bic_target - cwnd); + else + ca->cnt =3D 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 =3D=3D 0 && ca->cnt > 20) + ca->cnt =3D 20; /* increase cwnd 5% per RTT */ + +tcp_friendliness: + /* TCP Friendly */ + if (tcp_friendliness) { + u32 scale =3D beta_scale; + + delta =3D (cwnd * scale) >> 3; + while (ca->ack_cnt > delta) { /* update tcp cwnd */ + ca->ack_cnt -=3D delta; + ca->tcp_cwnd++; + } + + if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */ + delta =3D ca->tcp_cwnd - cwnd; + max_cnt =3D cwnd / delta; + if (ca->cnt > max_cnt) + ca->cnt =3D 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 =3D max(ca->cnt, 2U); +} + +__bpf_kfunc static void roccettcp_cong_avoid(struct sock *sk, u32 ack, + u32 acked) +{ + struct tcp_sock *tp =3D tcp_sk(sk); + struct roccettcp *ca =3D inet_csk_ca(sk); + + u32 now =3D jiffies_to_usecs(tcp_jiffies32); + u32 bw_limit_detect =3D 0; + u32 roccet_xj; + u32 jitter; + + if (ca->last_rtt > ca->curr_rtt) + jitter =3D ca->last_rtt - ca->curr_rtt; + else + jitter =3D 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) >=3D ca->ece_cwnd) + ca->ece_srrtt =3D 0; + } + + /* ROCCET drain. + * Do not increase the cwnd for 100ms after a roccet congestion event + */ + if (now - ca->roccet_last_event_time_us <=3D 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) >=3D ack_rate_diff_ss) || + (!tcp_is_cwnd_limited(sk) && tcp_in_slow_start(tp))) { + ca->epoch_start =3D 0; + + /* Handle initial slow start. Here we observe the most problems */ + if (tp->snd_ssthresh =3D=3D TCP_INFINITE_SSTHRESH) { + tcp_sk(sk)->snd_ssthresh =3D tcp_snd_cwnd(tp) / 2; + tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) / 2); + } else { + tcp_sk(sk)->snd_ssthresh =3D + 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 =3D now; + return; + } + + if (tcp_in_slow_start(tp)) { + acked =3D tcp_slow_start(tp, acked); + if (!acked) + return; + } + + if (ca->bw_limit.next_check =3D=3D 0) + ca->bw_limit.next_check =3D now + 5 * ca->curr_rtt; + + ca->bw_limit.sum_cwnd +=3D tcp_snd_cwnd(tp); + ca->bw_limit.sum_acked +=3D 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 >=3D + ack_rate_diff_ca) + bw_limit_detect =3D 1; + + /* reset struct and set next end of period */ + ca->bw_limit.sum_cwnd =3D 1; + + /* set to 1 to avoid division by zero */ + ca->bw_limit.sum_acked =3D 1; + ca->bw_limit.next_check =3D now + 5 * ca->curr_rtt; + } + + /* Respects the jitter of the connection and add it on top of the upper b= ound + * for the srRTT + */ + roccet_xj =3D ((jitter * 100) / ca->curr_min_rtt_timed.rtt) + + sr_rtt_upper_bound; + if (roccet_xj < sr_rtt_upper_bound) + roccet_xj =3D 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 =3D ca->ece_srrtt; + + if (ca->curr_srrtt > roccet_xj && (bw_limit_detect || ca->ece_srrtt > 0))= { + ca->epoch_start =3D 0; + ca->roccet_last_event_time_us =3D now; + ca->cnt =3D 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 =3D 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 =3D 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 fro= zen at + * an excessively high value. This is because slow start or HyStart massi= vely + * exceed the available bandwidth and leave the cwnd at an excessively hi= gh + * value. The cwnd cannot therefore be fully utilized because it is limit= ed 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 =3D tcp_sk(sk); + struct roccettcp *ca =3D 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 =3D 0; /* end of epoch */ + + /* Wmax and fast convergence */ + if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence) + ca->last_max_cwnd =3D + (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta)) / + (2 * BICTCP_BETA_SCALE); + else + ca->last_max_cwnd =3D 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 =3D inet_csk_ca(sk); + + if (new_state =3D=3D TCP_CA_Loss) + roccettcp_reset(ca); +} + +__bpf_kfunc static void roccettcp_acked(struct sock *sk, + const struct ack_sample *sample) +{ + struct roccettcp *ca =3D 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 =3D sample->rtt_us; + + if (delay =3D=3D 0) + delay =3D 1; + + /* first time call or link delay decreases */ + if (ca->delay_min =3D=3D 0 || ca->delay_min > delay) + ca->delay_min =3D delay; + + /* Get valid sample for roccet */ + if (sample->rtt_us > 0) { + ca->last_rtt =3D ca->curr_rtt; + ca->curr_rtt =3D sample->rtt_us; + } +} + +__bpf_kfunc static void roccet_in_ack_event(struct sock *sk, u32 flags) +{ + struct tcp_sock *tp =3D tcp_sk(sk); + struct roccettcp *ca =3D 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 =3D ca->curr_srrtt; + ca->ece_cwnd =3D tcp_snd_cwnd(tp); + } +} + +static struct tcp_congestion_ops roccet_tcp __read_mostly =3D { + .init =3D roccettcp_init, + .ssthresh =3D roccettcp_recalc_ssthresh, + .cong_avoid =3D roccettcp_cong_avoid, + .set_state =3D roccettcp_state, + .undo_cwnd =3D tcp_reno_undo_cwnd, + .cwnd_event =3D roccettcp_cwnd_event, + .pkts_acked =3D roccettcp_acked, + .in_ack_event =3D roccet_in_ack_event, + .owner =3D THIS_MODULE, + .name =3D "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 =3D { + .owner =3D THIS_MODULE, + .set =3D &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 =3D + 8 * (BICTCP_BETA_SCALE + beta) / 3 / (BICTCP_BETA_SCALE - beta); + + cube_rtt_scale =3D (bic_scale * 10); /* 1024*c/rtt */ + + /* calculate the "K" for (wmax-cwnd) =3D c/rtt * K^3 + * so K =3D cubic_root( (wmax-cwnd)*rtt/c ) + * the unit of K is bictcp_HZ=3D2^10, not HZ + * + * c =3D bic_scale >> 10 + * rtt =3D 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 =3D 1ull << (10 + 3 * BICTCP_HZ); /* 2^40 */ + + /* divide by bic_scale and by constant Srtt (100ms) */ + do_div(cube_factor, bic_scale * 10); + + ret =3D 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 + +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-Algor= ithm */ +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 epo= ch */ + 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 timestam= p */ + 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 */ --=20 2.43.0