I ran some BBR tests under different scenarios and I am concerned that under some conditions BBR can become very aggressive. It seems BBR flows can decide that losses are un-correlated to congestion, and when in this mode, they will maintain large cwnds regardless of the losses. In cases when BBR is wrong, it will starve non-BBR flows sharing the bottleneck. Im some of my tests even some BBR flows were starved when some flows got into this mode and others didn¹t.
I posted the report here: https://drive.google.com/open?id=0B4YZ_0yTgbJEa21CbUVLWFdrX2c - Lawrence On 9/19/16, 8:39 PM, "netdev-ow...@vger.kernel.org on behalf of Neal Cardwell" <netdev-ow...@vger.kernel.org on behalf of ncardw...@google.com> wrote: >This commit implements a new TCP congestion control algorithm: BBR >(Bottleneck Bandwidth and RTT). A detailed description of BBR will be >published in ACM Queue, Vol. 14 No. 5, September-October 2016, as >"BBR: Congestion-Based Congestion Control". > >BBR has significantly increased throughput and reduced latency for >connections on Google's internal backbone networks and google.com and >YouTube Web servers. > >BBR requires only changes on the sender side, not in the network or >the receiver side. Thus it can be incrementally deployed on today's >Internet, or in datacenters. > >The Internet has predominantly used loss-based congestion control >(largely Reno or CUBIC) since the 1980s, relying on packet loss as the >signal to slow down. While this worked well for many years, loss-based >congestion control is unfortunately out-dated in today's networks. On >today's Internet, loss-based congestion control causes the infamous >bufferbloat problem, often causing seconds of needless queuing delay, >since it fills the bloated buffers in many last-mile links. On today's >high-speed long-haul links using commodity switches with shallow >buffers, loss-based congestion control has abysmal throughput because >it over-reacts to losses caused by transient traffic bursts. > >In 1981 Kleinrock and Gale showed that the optimal operating point for >a network maximizes delivered bandwidth while minimizing delay and >loss, not only for single connections but for the network as a >whole. Finding that optimal operating point has been elusive, since >any single network measurement is ambiguous: network measurements are >the result of both bandwidth and propagation delay, and those two >cannot be measured simultaneously. > >While it is impossible to disambiguate any single bandwidth or RTT >measurement, a connection's behavior over time tells a clearer >story. BBR uses a measurement strategy designed to resolve this >ambiguity. It combines these measurements with a robust servo loop >using recent control systems advances to implement a distributed >congestion control algorithm that reacts to actual congestion, not >packet loss or transient queue delay, and is designed to converge with >high probability to a point near the optimal operating point. > >In a nutshell, BBR creates an explicit model of the network pipe by >sequentially probing the bottleneck bandwidth and RTT. On the arrival >of each ACK, BBR derives the current delivery rate of the last round >trip, and feeds it through a windowed max-filter to estimate the >bottleneck bandwidth. Conversely it uses a windowed min-filter to >estimate the round trip propagation delay. The max-filtered bandwidth >and min-filtered RTT estimates form BBR's model of the network pipe. > >Using its model, BBR sets control parameters to govern sending >behavior. The primary control is the pacing rate: BBR applies a gain >multiplier to transmit faster or slower than the observed bottleneck >bandwidth. The conventional congestion window (cwnd) is now the >secondary control; the cwnd is set to a small multiple of the >estimated BDP (bandwidth-delay product) in order to allow full >utilization and bandwidth probing while bounding the potential amount >of queue at the bottleneck. > >When a BBR connection starts, it enters STARTUP mode and applies a >high gain to perform an exponential search to quickly probe the >bottleneck bandwidth (doubling its sending rate each round trip, like >slow start). However, instead of continuing until it fills up the >buffer (i.e. a loss), or until delay or ACK spacing reaches some >threshold (like Hystart), it uses its model of the pipe to estimate >when that pipe is full: it estimates the pipe is full when it notices >the estimated bandwidth has stopped growing. At that point it exits >STARTUP and enters DRAIN mode, where it reduces its pacing rate to >drain the queue it estimates it has created. > >Then BBR enters steady state. In steady state, PROBE_BW mode cycles >between first pacing faster to probe for more bandwidth, then pacing >slower to drain any queue that created if no more bandwidth was >available, and then cruising at the estimated bandwidth to utilize the >pipe without creating excess queue. Occasionally, on an as-needed >basis, it sends significantly slower to probe for RTT (PROBE_RTT >mode). > >BBR has been fully deployed on Google's wide-area backbone networks >and we're experimenting with BBR on Google.com and YouTube on a global >scale. Replacing CUBIC with BBR has resulted in significant >improvements in network latency and application (RPC, browser, and >video) metrics. For more details please refer to our upcoming ACM >Queue publication. > >Example performance results, to illustrate the difference between BBR >and CUBIC: > >Resilience to random loss (e.g. from shallow buffers): > Consider a netperf TCP_STREAM test lasting 30 secs on an emulated > path with a 10Gbps bottleneck, 100ms RTT, and 1% packet loss > rate. CUBIC gets 3.27 Mbps, and BBR gets 9150 Mbps (2798x higher). > >Low latency with the bloated buffers common in today's last-mile links: > Consider a netperf TCP_STREAM test lasting 120 secs on an emulated > path with a 10Mbps bottleneck, 40ms RTT, and 1000-packet bottleneck > buffer. Both fully utilize the bottleneck bandwidth, but BBR > achieves this with a median RTT 25x lower (43 ms instead of 1.09 > secs). > >Our long-term goal is to improve the congestion control algorithms >used on the Internet. We are hopeful that BBR can help advance the >efforts toward this goal, and motivate the community to do further >research. > >Test results, performance evaluations, feedback, and BBR-related >discussions are very welcome in the public e-mail list for BBR: > > >https://urldefense.proofpoint.com/v2/url?u=https-3A__groups.google.com_for >um_-23-21forum_bbr-2Ddev&d=DQIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=pq_Mqvzfy-C8l >tkgyx1u_g&m=xV8BAzDZSWNmi4irvSU7Cnf_stojC7Qv3TSqkxYzMK0&s=mWB9nxnt76UWKkpT >0cioXxwy06b0evTHGgwlI3STNCI&e= > >NOTE: BBR *must* be used with the fq qdisc ("man tc-fq") with pacing >enabled, since pacing is integral to the BBR design and >implementation. BBR without pacing would not function properly, and >may incur unnecessary high packet loss rates. > >Signed-off-by: Van Jacobson <v...@google.com> >Signed-off-by: Neal Cardwell <ncardw...@google.com> >Signed-off-by: Yuchung Cheng <ych...@google.com> >Signed-off-by: Nandita Dukkipati <nandi...@google.com> >Signed-off-by: Eric Dumazet <eduma...@google.com> >Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com> >--- > include/uapi/linux/inet_diag.h | 13 + > net/ipv4/Kconfig | 18 + > net/ipv4/Makefile | 1 + > net/ipv4/tcp_bbr.c | 896 >+++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 928 insertions(+) > create mode 100644 net/ipv4/tcp_bbr.c > >diff --git a/include/uapi/linux/inet_diag.h >b/include/uapi/linux/inet_diag.h >index b5c366f..509cd96 100644 >--- a/include/uapi/linux/inet_diag.h >+++ b/include/uapi/linux/inet_diag.h >@@ -124,6 +124,7 @@ enum { > INET_DIAG_PEERS, > INET_DIAG_PAD, > INET_DIAG_MARK, >+ INET_DIAG_BBRINFO, > __INET_DIAG_MAX, > }; > >@@ -157,8 +158,20 @@ struct tcp_dctcp_info { > __u32 dctcp_ab_tot; > }; > >+/* INET_DIAG_BBRINFO */ >+ >+struct tcp_bbr_info { >+ /* u64 bw: max-filtered BW (app throughput) estimate in Byte per sec: */ >+ __u32 bbr_bw_lo; /* lower 32 bits of bw */ >+ __u32 bbr_bw_hi; /* upper 32 bits of bw */ >+ __u32 bbr_min_rtt; /* min-filtered RTT in uSec */ >+ __u32 bbr_pacing_gain; /* pacing gain shifted left 8 bits */ >+ __u32 bbr_cwnd_gain; /* cwnd gain shifted left 8 bits */ >+}; >+ > union tcp_cc_info { > struct tcpvegas_info vegas; > struct tcp_dctcp_info dctcp; >+ struct tcp_bbr_info bbr; > }; > #endif /* _UAPI_INET_DIAG_H_ */ >diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig >index 50d6a9b..300b068 100644 >--- a/net/ipv4/Kconfig >+++ b/net/ipv4/Kconfig >@@ -640,6 +640,21 @@ config TCP_CONG_CDG > D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using > delay gradients." In Networking 2011. Preprint: >https://urldefense.proofpoint.com/v2/url?u=http-3A__goo.gl_No3vdg&d=DQIBAg >&c=5VD0RTtNlTh3ycd41b3MUw&r=pq_Mqvzfy-C8ltkgyx1u_g&m=xV8BAzDZSWNmi4irvSU7C >nf_stojC7Qv3TSqkxYzMK0&s=cVqj8M0_43G6FqE2LfEGLAe5pfUieb8_YYe2TquWgSA&e= > >+config TCP_CONG_BBR >+ tristate "BBR TCP" >+ default n >+ ---help--- >+ >+ BBR (Bottleneck Bandwidth and RTT) TCP congestion control aims to >+ maximize network utilization and minimize queues. It builds an explicit >+ model of the the bottleneck delivery rate and path round-trip >+ propagation delay. It tolerates packet loss and delay unrelated to >+ congestion. It can operate over LAN, WAN, cellular, wifi, or cable >+ modem links. It can coexist with flows that use loss-based congestion >+ control, and can operate with shallow buffers, deep buffers, >+ bufferbloat, policers, or AQM schemes that do not provide a delay >+ signal. It requires the fq ("Fair Queue") pacing packet scheduler. >+ > choice > prompt "Default TCP congestion control" > default DEFAULT_CUBIC >@@ -674,6 +689,9 @@ choice > config DEFAULT_CDG > bool "CDG" if TCP_CONG_CDG=y > >+ config DEFAULT_BBR >+ bool "BBR" if TCP_CONG_BBR=y >+ > config DEFAULT_RENO > bool "Reno" > endchoice >diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile >index 9cfff1a..bc6a6c8 100644 >--- a/net/ipv4/Makefile >+++ b/net/ipv4/Makefile >@@ -41,6 +41,7 @@ obj-$(CONFIG_INET_DIAG) += inet_diag.o > obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o > obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o > obj-$(CONFIG_NET_TCPPROBE) += tcp_probe.o >+obj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o > obj-$(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_bbr.c b/net/ipv4/tcp_bbr.c >new file mode 100644 >index 0000000..0ea66c2 >--- /dev/null >+++ b/net/ipv4/tcp_bbr.c >@@ -0,0 +1,896 @@ >+/* Bottleneck Bandwidth and RTT (BBR) congestion control >+ * >+ * BBR congestion control computes the sending rate based on the delivery >+ * rate (throughput) estimated from ACKs. In a nutshell: >+ * >+ * On each ACK, update our model of the network path: >+ * bottleneck_bandwidth = windowed_max(delivered / elapsed, 10 >round trips) >+ * min_rtt = windowed_min(rtt, 10 seconds) >+ * pacing_rate = pacing_gain * bottleneck_bandwidth >+ * cwnd = max(cwnd_gain * bottleneck_bandwidth * min_rtt, 4) >+ * >+ * The core algorithm does not react directly to packet losses or delays, >+ * although BBR may adjust the size of next send per ACK when loss is >+ * observed, or adjust the sending rate if it estimates there is a >+ * traffic policer, in order to keep the drop rate reasonable. >+ * >+ * BBR is described in detail in: >+ * "BBR: Congestion-Based Congestion Control", >+ * Neal Cardwell, Yuchung Cheng, C. Stephen Gunn, Soheil Hassas >Yeganeh, >+ * Van Jacobson. ACM Queue, Vol. 14 No. 5, September-October 2016. >+ * >+ * There is a public e-mail list for discussing BBR development and >testing: >+ * >https://urldefense.proofpoint.com/v2/url?u=https-3A__groups.google.com_for >um_-23-21forum_bbr-2Ddev&d=DQIBAg&c=5VD0RTtNlTh3ycd41b3MUw&r=pq_Mqvzfy-C8l >tkgyx1u_g&m=xV8BAzDZSWNmi4irvSU7Cnf_stojC7Qv3TSqkxYzMK0&s=mWB9nxnt76UWKkpT >0cioXxwy06b0evTHGgwlI3STNCI&e= >+ * >+ * NOTE: BBR *must* be used with the fq qdisc ("man tc-fq") with pacing >enabled, >+ * since pacing is integral to the BBR design and implementation. >+ * BBR without pacing would not function properly, and may incur >unnecessary >+ * high packet loss rates. >+ */ >+#include <linux/module.h> >+#include <net/tcp.h> >+#include <linux/inet_diag.h> >+#include <linux/inet.h> >+#include <linux/random.h> >+#include <linux/win_minmax.h> >+ >+/* Scale factor for rate in pkt/uSec unit to avoid truncation in >bandwidth >+ * estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps. >+ * This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a >u32. >+ * Since the minimum window is >=4 packets, the lower bound isn't >+ * an issue. The upper bound isn't an issue with existing technologies. >+ */ >+#define BW_SCALE 24 >+#define BW_UNIT (1 << BW_SCALE) >+ >+#define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) >*/ >+#define BBR_UNIT (1 << BBR_SCALE) >+ >+/* BBR has the following modes for deciding how fast to send: */ >+enum bbr_mode { >+ BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */ >+ BBR_DRAIN, /* drain any queue created during startup */ >+ BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */ >+ BBR_PROBE_RTT, /* cut cwnd to min to probe min_rtt */ >+}; >+ >+/* BBR congestion control block */ >+struct bbr { >+ u32 min_rtt_us; /* min RTT in min_rtt_win_sec window */ >+ u32 min_rtt_stamp; /* timestamp of min_rtt_us */ >+ u32 probe_rtt_done_stamp; /* end time for BBR_PROBE_RTT mode */ >+ struct minmax bw; /* Max recent delivery rate in pkts/uS << 24 */ >+ u32 rtt_cnt; /* count of packet-timed rounds elapsed */ >+ u32 next_rtt_delivered; /* scb->tx.delivered at end of round */ >+ struct skb_mstamp cycle_mstamp; /* time of this cycle phase start */ >+ u32 mode:3, /* current bbr_mode in state machine */ >+ prev_ca_state:3, /* CA state on previous ACK */ >+ packet_conservation:1, /* use packet conservation? */ >+ restore_cwnd:1, /* decided to revert cwnd to old value */ >+ round_start:1, /* start of packet-timed tx->ack round? */ >+ tso_segs_goal:7, /* segments we want in each skb we send */ >+ idle_restart:1, /* restarting after idle? */ >+ probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */ >+ unused:5, >+ lt_is_sampling:1, /* taking long-term ("LT") samples now? */ >+ lt_rtt_cnt:7, /* round trips in long-term interval */ >+ lt_use_bw:1; /* use lt_bw as our bw estimate? */ >+ u32 lt_bw; /* LT est delivery rate in pkts/uS << 24 */ >+ u32 lt_last_delivered; /* LT intvl start: tp->delivered */ >+ u32 lt_last_stamp; /* LT intvl start: tp->delivered_mstamp */ >+ u32 lt_last_lost; /* LT intvl start: tp->lost */ >+ u32 pacing_gain:10, /* current gain for setting pacing rate */ >+ cwnd_gain:10, /* current gain for setting cwnd */ >+ full_bw_cnt:3, /* number of rounds without large bw gains */ >+ cycle_idx:3, /* current index in pacing_gain cycle array */ >+ unused_b:6; >+ u32 prior_cwnd; /* prior cwnd upon entering loss recovery */ >+ u32 full_bw; /* recent bw, to estimate if pipe is full */ >+}; >+ >+#define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */ >+ >+/* Window length of bw filter (in rounds): */ >+static const int bbr_bw_rtts = CYCLE_LEN + 2; >+/* Window length of min_rtt filter (in sec): */ >+static const u32 bbr_min_rtt_win_sec = 10; >+/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT >mode: */ >+static const u32 bbr_probe_rtt_mode_ms = 200; >+/* Skip TSO below the following bandwidth (bits/sec): */ >+static const int bbr_min_tso_rate = 1200000; >+ >+/* We use a high_gain value of 2/ln(2) because it's the smallest pacing >gain >+ * that will allow a smoothly increasing pacing rate that will double >each RTT >+ * and send the same number of packets per RTT that an un-paced, >slow-starting >+ * Reno or CUBIC flow would: >+ */ >+static const int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1; >+/* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to >typically drain >+ * the queue created in BBR_STARTUP in a single round: >+ */ >+static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885; >+/* The gain for deriving steady-state cwnd tolerates delayed/stretched >ACKs: */ >+static const int bbr_cwnd_gain = BBR_UNIT * 2; >+/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share >bw: */ >+static const int bbr_pacing_gain[] = { >+ BBR_UNIT * 5 / 4, /* probe for more available bw */ >+ BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */ >+ BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */ >+ BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */ >+}; >+/* Randomize the starting gain cycling phase over N phases: */ >+static const u32 bbr_cycle_rand = 7; >+ >+/* Try to keep at least this many packets in flight, if things go >smoothly. For >+ * smooth functioning, a sliding window protocol ACKing every other >packet >+ * needs at least 4 packets in flight: >+ */ >+static const u32 bbr_cwnd_min_target = 4; >+ >+/* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */ >+/* If bw has increased significantly (1.25x), there may be more bw >available: */ >+static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4; >+/* But after 3 rounds w/o significant bw growth, estimate pipe is full: >*/ >+static const u32 bbr_full_bw_cnt = 3; >+ >+/* "long-term" ("LT") bandwidth estimator parameters... */ >+/* The minimum number of rounds in an LT bw sampling interval: */ >+static const u32 bbr_lt_intvl_min_rtts = 4; >+/* If lost/delivered ratio > 20%, interval is "lossy" and we may be >policed: */ >+static const u32 bbr_lt_loss_thresh = 50; >+/* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */ >+static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8; >+/* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": >*/ >+static const u32 bbr_lt_bw_diff = 4000 / 8; >+/* If we estimate we're policed, use lt_bw for this many round trips: */ >+static const u32 bbr_lt_bw_max_rtts = 48; >+ >+/* Do we estimate that STARTUP filled the pipe? */ >+static bool bbr_full_bw_reached(const struct sock *sk) >+{ >+ const struct bbr *bbr = inet_csk_ca(sk); >+ >+ return bbr->full_bw_cnt >= bbr_full_bw_cnt; >+} >+ >+/* Return the windowed max recent bandwidth sample, in pkts/uS << >BW_SCALE. */ >+static u32 bbr_max_bw(const struct sock *sk) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ return minmax_get(&bbr->bw); >+} >+ >+/* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */ >+static u32 bbr_bw(const struct sock *sk) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ return bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk); >+} >+ >+/* Return rate in bytes per second, optionally with a gain. >+ * The order here is chosen carefully to avoid overflow of u64. This >should >+ * work for input rates of up to 2.9Tbit/sec and gain of 2.89x. >+ */ >+static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain) >+{ >+ rate *= tcp_mss_to_mtu(sk, tcp_sk(sk)->mss_cache); >+ rate *= gain; >+ rate >>= BBR_SCALE; >+ rate *= USEC_PER_SEC; >+ return rate >> BW_SCALE; >+} >+ >+/* Pace using current bw estimate and a gain factor. In order to help >drive the >+ * network toward lower queues while maintaining high utilization and low >+ * latency, the average pacing rate aims to be slightly (~1%) lower than >the >+ * estimated bandwidth. This is an important aspect of the design. In >this >+ * implementation this slightly lower pacing rate is achieved implicitly >by not >+ * including link-layer headers in the packet size used for the pacing >rate. >+ */ >+static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ u64 rate = bw; >+ >+ rate = bbr_rate_bytes_per_sec(sk, rate, gain); >+ rate = min_t(u64, rate, sk->sk_max_pacing_rate); >+ if (bbr->mode != BBR_STARTUP || rate > sk->sk_pacing_rate) >+ sk->sk_pacing_rate = rate; >+} >+ >+/* Return count of segments we want in the skbs we send, or 0 for >default. */ >+static u32 bbr_tso_segs_goal(struct sock *sk) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ return bbr->tso_segs_goal; >+} >+ >+static void bbr_set_tso_segs_goal(struct sock *sk) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 min_segs; >+ >+ min_segs = sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2; >+ bbr->tso_segs_goal = min(tcp_tso_autosize(sk, tp->mss_cache, min_segs), >+ 0x7FU); >+} >+ >+/* Save "last known good" cwnd so we can restore it after losses or >PROBE_RTT */ >+static void bbr_save_cwnd(struct sock *sk) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT) >+ bbr->prior_cwnd = tp->snd_cwnd; /* this cwnd is good enough */ >+ else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */ >+ bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd); >+} >+ >+static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ if (event == CA_EVENT_TX_START && tp->app_limited) { >+ bbr->idle_restart = 1; >+ /* Avoid pointless buffer overflows: pace at est. bw if we don't >+ * need more speed (we're restarting from idle and app-limited). >+ */ >+ if (bbr->mode == BBR_PROBE_BW) >+ bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT); >+ } >+} >+ >+/* Find target cwnd. Right-size the cwnd based on min RTT and the >+ * estimated bottleneck bandwidth: >+ * >+ * cwnd = bw * min_rtt * gain = BDP * gain >+ * >+ * The key factor, gain, controls the amount of queue. While a small gain >+ * builds a smaller queue, it becomes more vulnerable to noise in RTT >+ * measurements (e.g., delayed ACKs or other ACK compression effects). >This >+ * noise may cause BBR to under-estimate the rate. >+ * >+ * To achieve full performance in high-speed paths, we budget enough >cwnd to >+ * fit full-sized skbs in-flight on both end hosts to fully utilize the >path: >+ * - one skb in sending host Qdisc, >+ * - one skb in sending host TSO/GSO engine >+ * - one skb being received by receiver host LRO/GRO/delayed-ACK engine >+ * Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd >because >+ * in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets, >+ * which allows 2 outstanding 2-packet sequences, to try to keep pipe >+ * full even with ACK-every-other-packet delayed ACKs. >+ */ >+static u32 bbr_target_cwnd(struct sock *sk, u32 bw, int gain) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 cwnd; >+ u64 w; >+ >+ /* If we've never had a valid RTT sample, cap cwnd at the initial >+ * default. This should only happen when the connection is not using TCP >+ * timestamps and has retransmitted all of the SYN/SYNACK/data packets >+ * ACKed so far. In this case, an RTO can cut cwnd to 1, in which >+ * case we need to slow-start up toward something safe: TCP_INIT_CWND. >+ */ >+ if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */ >+ return TCP_INIT_CWND; /* be safe: cap at default initial cwnd*/ >+ >+ w = (u64)bw * bbr->min_rtt_us; >+ >+ /* Apply a gain to the given value, then remove the BW_SCALE shift. */ >+ cwnd = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; >+ >+ /* Allow enough full-sized skbs in flight to utilize end systems. */ >+ cwnd += 3 * bbr->tso_segs_goal; >+ >+ /* Reduce delayed ACKs by rounding up cwnd to the next even number. */ >+ cwnd = (cwnd + 1) & ~1U; >+ >+ return cwnd; >+} >+ >+/* An optimization in BBR to reduce losses: On the first round of >recovery, we >+ * follow the packet conservation principle: send P packets per P >packets acked. >+ * After that, we slow-start and send at most 2*P packets per P packets >acked. >+ * After recovery finishes, or upon undo, we restore the cwnd we had when >+ * recovery started (capped by the target cwnd based on estimated BDP). >+ * >+ * TODO(ycheng/ncardwell): implement a rate-based approach. >+ */ >+static bool bbr_set_cwnd_to_recover_or_restore( >+ struct sock *sk, const struct rate_sample *rs, u32 acked, u32 *new_cwnd) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state; >+ u32 cwnd = tp->snd_cwnd; >+ >+ /* An ACK for P pkts should release at most 2*P packets. We do this >+ * in two steps. First, here we deduct the number of lost packets. >+ * Then, in bbr_set_cwnd() we slow start up toward the target cwnd. >+ */ >+ if (rs->losses > 0) >+ cwnd = max_t(s32, cwnd - rs->losses, 1); >+ >+ if (state == TCP_CA_Recovery && prev_state != TCP_CA_Recovery) { >+ /* Starting 1st round of Recovery, so do packet conservation. */ >+ bbr->packet_conservation = 1; >+ bbr->next_rtt_delivered = tp->delivered; /* start round now */ >+ /* Cut unused cwnd from app behavior, TSQ, or TSO deferral: */ >+ cwnd = tcp_packets_in_flight(tp) + acked; >+ } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) { >+ /* Exiting loss recovery; restore cwnd saved before recovery. */ >+ bbr->restore_cwnd = 1; >+ bbr->packet_conservation = 0; >+ } >+ bbr->prev_ca_state = state; >+ >+ if (bbr->restore_cwnd) { >+ /* Restore cwnd after exiting loss recovery or PROBE_RTT. */ >+ cwnd = max(cwnd, bbr->prior_cwnd); >+ bbr->restore_cwnd = 0; >+ } >+ >+ if (bbr->packet_conservation) { >+ *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked); >+ return true; /* yes, using packet conservation */ >+ } >+ *new_cwnd = cwnd; >+ return false; >+} >+ >+/* Slow-start up toward target cwnd (if bw estimate is growing, or >packet loss >+ * has drawn us down below target), or snap down to target if we're >above it. >+ */ >+static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs, >+ u32 acked, u32 bw, int gain) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 cwnd = 0, target_cwnd = 0; >+ >+ if (!acked) >+ return; >+ >+ if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) >+ goto done; >+ >+ /* If we're below target cwnd, slow start cwnd toward target cwnd. */ >+ target_cwnd = bbr_target_cwnd(sk, bw, gain); >+ if (bbr_full_bw_reached(sk)) /* only cut cwnd if we filled the pipe */ >+ cwnd = min(cwnd + acked, target_cwnd); >+ else if (cwnd < target_cwnd || tp->delivered < TCP_INIT_CWND) >+ cwnd = cwnd + acked; >+ cwnd = max(cwnd, bbr_cwnd_min_target); >+ >+done: >+ tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); /* apply global cap */ >+ if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */ >+ tp->snd_cwnd = min(tp->snd_cwnd, bbr_cwnd_min_target); >+} >+ >+/* End cycle phase if it's time and/or we hit the phase's in-flight >target. */ >+static bool bbr_is_next_cycle_phase(struct sock *sk, >+ const struct rate_sample *rs) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ bool is_full_length = >+ skb_mstamp_us_delta(&tp->delivered_mstamp, &bbr->cycle_mstamp) > >+ bbr->min_rtt_us; >+ u32 inflight, bw; >+ >+ /* The pacing_gain of 1.0 paces at the estimated bw to try to fully >+ * use the pipe without increasing the queue. >+ */ >+ if (bbr->pacing_gain == BBR_UNIT) >+ return is_full_length; /* just use wall clock time */ >+ >+ inflight = rs->prior_in_flight; /* what was in-flight before ACK? */ >+ bw = bbr_max_bw(sk); >+ >+ /* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at >+ * least pacing_gain*BDP; this may take more than min_rtt if min_rtt is >+ * small (e.g. on a LAN). We do not persist if packets are lost, since >+ * a path with small buffers may not hold that much. >+ */ >+ if (bbr->pacing_gain > BBR_UNIT) >+ return is_full_length && >+ (rs->losses || /* perhaps pacing_gain*BDP won't fit */ >+ inflight >= bbr_target_cwnd(sk, bw, bbr->pacing_gain)); >+ >+ /* A pacing_gain < 1.0 tries to drain extra queue we added if bw >+ * probing didn't find more bw. If inflight falls to match BDP then we >+ * estimate queue is drained; persisting would underutilize the pipe. >+ */ >+ return is_full_length || >+ inflight <= bbr_target_cwnd(sk, bw, BBR_UNIT); >+} >+ >+static void bbr_advance_cycle_phase(struct sock *sk) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1); >+ bbr->cycle_mstamp = tp->delivered_mstamp; >+ bbr->pacing_gain = bbr_pacing_gain[bbr->cycle_idx]; >+} >+ >+/* Gain cycling: cycle pacing gain to converge to fair share of >available bw. */ >+static void bbr_update_cycle_phase(struct sock *sk, >+ const struct rate_sample *rs) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ if ((bbr->mode == BBR_PROBE_BW) && !bbr->lt_use_bw && >+ bbr_is_next_cycle_phase(sk, rs)) >+ bbr_advance_cycle_phase(sk); >+} >+ >+static void bbr_reset_startup_mode(struct sock *sk) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ bbr->mode = BBR_STARTUP; >+ bbr->pacing_gain = bbr_high_gain; >+ bbr->cwnd_gain = bbr_high_gain; >+} >+ >+static void bbr_reset_probe_bw_mode(struct sock *sk) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ bbr->mode = BBR_PROBE_BW; >+ bbr->pacing_gain = BBR_UNIT; >+ bbr->cwnd_gain = bbr_cwnd_gain; >+ bbr->cycle_idx = CYCLE_LEN - 1 - prandom_u32_max(bbr_cycle_rand); >+ bbr_advance_cycle_phase(sk); /* flip to next phase of gain cycle */ >+} >+ >+static void bbr_reset_mode(struct sock *sk) >+{ >+ if (!bbr_full_bw_reached(sk)) >+ bbr_reset_startup_mode(sk); >+ else >+ bbr_reset_probe_bw_mode(sk); >+} >+ >+/* Start a new long-term sampling interval. */ >+static void bbr_reset_lt_bw_sampling_interval(struct sock *sk) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ bbr->lt_last_stamp = tp->delivered_mstamp.stamp_jiffies; >+ bbr->lt_last_delivered = tp->delivered; >+ bbr->lt_last_lost = tp->lost; >+ bbr->lt_rtt_cnt = 0; >+} >+ >+/* Completely reset long-term bandwidth sampling. */ >+static void bbr_reset_lt_bw_sampling(struct sock *sk) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ bbr->lt_bw = 0; >+ bbr->lt_use_bw = 0; >+ bbr->lt_is_sampling = false; >+ bbr_reset_lt_bw_sampling_interval(sk); >+} >+ >+/* Long-term bw sampling interval is done. Estimate whether we're >policed. */ >+static void bbr_lt_bw_interval_done(struct sock *sk, u32 bw) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 diff; >+ >+ if (bbr->lt_bw) { /* do we have bw from a previous interval? */ >+ /* Is new bw close to the lt_bw from the previous interval? */ >+ diff = abs(bw - bbr->lt_bw); >+ if ((diff * BBR_UNIT <= bbr_lt_bw_ratio * bbr->lt_bw) || >+ (bbr_rate_bytes_per_sec(sk, diff, BBR_UNIT) <= >+ bbr_lt_bw_diff)) { >+ /* All criteria are met; estimate we're policed. */ >+ bbr->lt_bw = (bw + bbr->lt_bw) >> 1; /* avg 2 intvls */ >+ bbr->lt_use_bw = 1; >+ bbr->pacing_gain = BBR_UNIT; /* try to avoid drops */ >+ bbr->lt_rtt_cnt = 0; >+ return; >+ } >+ } >+ bbr->lt_bw = bw; >+ bbr_reset_lt_bw_sampling_interval(sk); >+} >+ >+/* Token-bucket traffic policers are common (see "An Internet-Wide >Analysis of >+ * Traffic Policing", SIGCOMM 2016). BBR detects token-bucket policers >and >+ * explicitly models their policed rate, to reduce unnecessary losses. We >+ * estimate that we're policed if we see 2 consecutive sampling >intervals with >+ * consistent throughput and high packet loss. If we think we're being >policed, >+ * set lt_bw to the "long-term" average delivery rate from those 2 >intervals. >+ */ >+static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample >*rs) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 lost, delivered; >+ u64 bw; >+ s32 t; >+ >+ if (bbr->lt_use_bw) { /* already using long-term rate, lt_bw? */ >+ if (bbr->mode == BBR_PROBE_BW && bbr->round_start && >+ ++bbr->lt_rtt_cnt >= bbr_lt_bw_max_rtts) { >+ bbr_reset_lt_bw_sampling(sk); /* stop using lt_bw */ >+ bbr_reset_probe_bw_mode(sk); /* restart gain cycling */ >+ } >+ return; >+ } >+ >+ /* Wait for the first loss before sampling, to let the policer exhaust >+ * its tokens and estimate the steady-state rate allowed by the policer. >+ * Starting samples earlier includes bursts that over-estimate the bw. >+ */ >+ if (!bbr->lt_is_sampling) { >+ if (!rs->losses) >+ return; >+ bbr_reset_lt_bw_sampling_interval(sk); >+ bbr->lt_is_sampling = true; >+ } >+ >+ /* To avoid underestimates, reset sampling if we run out of data. */ >+ if (rs->is_app_limited) { >+ bbr_reset_lt_bw_sampling(sk); >+ return; >+ } >+ >+ if (bbr->round_start) >+ bbr->lt_rtt_cnt++; /* count round trips in this interval */ >+ if (bbr->lt_rtt_cnt < bbr_lt_intvl_min_rtts) >+ return; /* sampling interval needs to be longer */ >+ if (bbr->lt_rtt_cnt > 4 * bbr_lt_intvl_min_rtts) { >+ bbr_reset_lt_bw_sampling(sk); /* interval is too long */ >+ return; >+ } >+ >+ /* End sampling interval when a packet is lost, so we estimate the >+ * policer tokens were exhausted. Stopping the sampling before the >+ * tokens are exhausted under-estimates the policed rate. >+ */ >+ if (!rs->losses) >+ return; >+ >+ /* Calculate packets lost and delivered in sampling interval. */ >+ lost = tp->lost - bbr->lt_last_lost; >+ delivered = tp->delivered - bbr->lt_last_delivered; >+ /* Is loss rate (lost/delivered) >= lt_loss_thresh? If not, wait. */ >+ if (!delivered || (lost << BBR_SCALE) < bbr_lt_loss_thresh * delivered) >+ return; >+ >+ /* Find average delivery rate in this sampling interval. */ >+ t = (s32)(tp->delivered_mstamp.stamp_jiffies - bbr->lt_last_stamp); >+ if (t < 1) >+ return; /* interval is less than one jiffy, so wait */ >+ t = jiffies_to_usecs(t); >+ /* Interval long enough for jiffies_to_usecs() to return a bogus 0? */ >+ if (t < 1) { >+ bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */ >+ return; >+ } >+ bw = (u64)delivered * BW_UNIT; >+ do_div(bw, t); >+ bbr_lt_bw_interval_done(sk, bw); >+} >+ >+/* Estimate the bandwidth based on how fast packets are delivered */ >+static void bbr_update_bw(struct sock *sk, const struct rate_sample *rs) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u64 bw; >+ >+ bbr->round_start = 0; >+ if (rs->delivered < 0 || rs->interval_us <= 0) >+ return; /* Not a valid observation */ >+ >+ /* See if we've reached the next RTT */ >+ if (!before(rs->prior_delivered, bbr->next_rtt_delivered)) { >+ bbr->next_rtt_delivered = tp->delivered; >+ bbr->rtt_cnt++; >+ bbr->round_start = 1; >+ bbr->packet_conservation = 0; >+ } >+ >+ bbr_lt_bw_sampling(sk, rs); >+ >+ /* Divide delivered by the interval to find a (lower bound) bottleneck >+ * bandwidth sample. Delivered is in packets and interval_us in uS and >+ * ratio will be <<1 for most connections. So delivered is first scaled. >+ */ >+ bw = (u64)rs->delivered * BW_UNIT; >+ do_div(bw, rs->interval_us); >+ >+ /* If this sample is application-limited, it is likely to have a very >+ * low delivered count that represents application behavior rather than >+ * the available network rate. Such a sample could drag down estimated >+ * bw, causing needless slow-down. Thus, to continue to send at the >+ * last measured network rate, we filter out app-limited samples unless >+ * they describe the path bw at least as well as our bw model. >+ * >+ * So the goal during app-limited phase is to proceed with the best >+ * network rate no matter how long. We automatically leave this >+ * phase when app writes faster than the network can deliver :) >+ */ >+ if (!rs->is_app_limited || bw >= bbr_max_bw(sk)) { >+ /* Incorporate new sample into our max bw filter. */ >+ minmax_running_max(&bbr->bw, bbr_bw_rtts, bbr->rtt_cnt, bw); >+ } >+} >+ >+/* Estimate when the pipe is full, using the change in delivery rate: BBR >+ * estimates that STARTUP filled the pipe if the estimated bw hasn't >changed by >+ * at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) >non-app-limited >+ * rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill >the >+ * higher rwin, 3: we get higher delivery rate samples. Or transient >+ * cross-traffic or radio noise can go away. CUBIC Hystart shares a >similar >+ * design goal, but uses delay and inter-ACK spacing instead of >bandwidth. >+ */ >+static void bbr_check_full_bw_reached(struct sock *sk, >+ const struct rate_sample *rs) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 bw_thresh; >+ >+ if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited) >+ return; >+ >+ bw_thresh = (u64)bbr->full_bw * bbr_full_bw_thresh >> BBR_SCALE; >+ if (bbr_max_bw(sk) >= bw_thresh) { >+ bbr->full_bw = bbr_max_bw(sk); >+ bbr->full_bw_cnt = 0; >+ return; >+ } >+ ++bbr->full_bw_cnt; >+} >+ >+/* If pipe is probably full, drain the queue and then enter >steady-state. */ >+static void bbr_check_drain(struct sock *sk, const struct rate_sample >*rs) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) { >+ bbr->mode = BBR_DRAIN; /* drain queue we created */ >+ bbr->pacing_gain = bbr_drain_gain; /* pace slow to drain */ >+ bbr->cwnd_gain = bbr_high_gain; /* maintain cwnd */ >+ } /* fall through to check if in-flight is already small: */ >+ if (bbr->mode == BBR_DRAIN && >+ tcp_packets_in_flight(tcp_sk(sk)) <= >+ bbr_target_cwnd(sk, bbr_max_bw(sk), BBR_UNIT)) >+ bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ >+} >+ >+/* The goal of PROBE_RTT mode is to have BBR flows cooperatively and >+ * periodically drain the bottleneck queue, to converge to measure the >true >+ * min_rtt (unloaded propagation delay). This allows the flows to keep >queues >+ * small (reducing queuing delay and packet loss) and achieve fairness >among >+ * BBR flows. >+ * >+ * The min_rtt filter window is 10 seconds. When the min_rtt estimate >expires, >+ * we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 >packets. >+ * After at least bbr_probe_rtt_mode_ms=200ms and at least one >packet-timed >+ * round trip elapsed with that flight size <= 4, we leave PROBE_RTT >mode and >+ * re-enter the previous mode. BBR uses 200ms to approximately bound the >+ * performance penalty of PROBE_RTT's cwnd capping to roughly 2% >(200ms/10s). >+ * >+ * Note that flows need only pay 2% if they are busy sending over the >last 10 >+ * seconds. Interactive applications (e.g., Web, RPCs, video chunks) >often have >+ * natural silences or low-rate periods within 10 seconds where the rate >is low >+ * enough for long enough to drain its queue in the bottleneck. We pick >up >+ * these min RTT measurements opportunistically with our min_rtt filter. >:-) >+ */ >+static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample >*rs) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ bool filter_expired; >+ >+ /* Track min RTT seen in the min_rtt_win_sec filter window: */ >+ filter_expired = after(tcp_time_stamp, >+ bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); >+ if (rs->rtt_us >= 0 && >+ (rs->rtt_us <= bbr->min_rtt_us || filter_expired)) { >+ bbr->min_rtt_us = rs->rtt_us; >+ bbr->min_rtt_stamp = tcp_time_stamp; >+ } >+ >+ if (bbr_probe_rtt_mode_ms > 0 && filter_expired && >+ !bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) { >+ bbr->mode = BBR_PROBE_RTT; /* dip, drain queue */ >+ bbr->pacing_gain = BBR_UNIT; >+ bbr->cwnd_gain = BBR_UNIT; >+ bbr_save_cwnd(sk); /* note cwnd so we can restore it */ >+ bbr->probe_rtt_done_stamp = 0; >+ } >+ >+ if (bbr->mode == BBR_PROBE_RTT) { >+ /* Ignore low rate samples during this mode. */ >+ tp->app_limited = >+ (tp->delivered + tcp_packets_in_flight(tp)) ? : 1; >+ /* Maintain min packets in flight for max(200 ms, 1 round). */ >+ if (!bbr->probe_rtt_done_stamp && >+ tcp_packets_in_flight(tp) <= bbr_cwnd_min_target) { >+ bbr->probe_rtt_done_stamp = tcp_time_stamp + >+ msecs_to_jiffies(bbr_probe_rtt_mode_ms); >+ bbr->probe_rtt_round_done = 0; >+ bbr->next_rtt_delivered = tp->delivered; >+ } else if (bbr->probe_rtt_done_stamp) { >+ if (bbr->round_start) >+ bbr->probe_rtt_round_done = 1; >+ if (bbr->probe_rtt_round_done && >+ after(tcp_time_stamp, bbr->probe_rtt_done_stamp)) { >+ bbr->min_rtt_stamp = tcp_time_stamp; >+ bbr->restore_cwnd = 1; /* snap to prior_cwnd */ >+ bbr_reset_mode(sk); >+ } >+ } >+ } >+ bbr->idle_restart = 0; >+} >+ >+static void bbr_update_model(struct sock *sk, const struct rate_sample >*rs) >+{ >+ bbr_update_bw(sk, rs); >+ bbr_update_cycle_phase(sk, rs); >+ bbr_check_full_bw_reached(sk, rs); >+ bbr_check_drain(sk, rs); >+ bbr_update_min_rtt(sk, rs); >+} >+ >+static void bbr_main(struct sock *sk, const struct rate_sample *rs) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ u32 bw; >+ >+ bbr_update_model(sk, rs); >+ >+ bw = bbr_bw(sk); >+ bbr_set_pacing_rate(sk, bw, bbr->pacing_gain); >+ bbr_set_tso_segs_goal(sk); >+ bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain); >+} >+ >+static void bbr_init(struct sock *sk) >+{ >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u64 bw; >+ >+ bbr->prior_cwnd = 0; >+ bbr->tso_segs_goal = 0; /* default segs per skb until first ACK */ >+ bbr->rtt_cnt = 0; >+ bbr->next_rtt_delivered = 0; >+ bbr->prev_ca_state = TCP_CA_Open; >+ bbr->packet_conservation = 0; >+ >+ bbr->probe_rtt_done_stamp = 0; >+ bbr->probe_rtt_round_done = 0; >+ bbr->min_rtt_us = tcp_min_rtt(tp); >+ bbr->min_rtt_stamp = tcp_time_stamp; >+ >+ minmax_reset(&bbr->bw, bbr->rtt_cnt, 0); /* init max bw to 0 */ >+ >+ /* Initialize pacing rate to: high_gain * init_cwnd / RTT. */ >+ bw = (u64)tp->snd_cwnd * BW_UNIT; >+ do_div(bw, (tp->srtt_us >> 3) ? : USEC_PER_MSEC); >+ sk->sk_pacing_rate = 0; /* force an update of sk_pacing_rate */ >+ bbr_set_pacing_rate(sk, bw, bbr_high_gain); >+ >+ bbr->restore_cwnd = 0; >+ bbr->round_start = 0; >+ bbr->idle_restart = 0; >+ bbr->full_bw = 0; >+ bbr->full_bw_cnt = 0; >+ bbr->cycle_mstamp.v64 = 0; >+ bbr->cycle_idx = 0; >+ bbr_reset_lt_bw_sampling(sk); >+ bbr_reset_startup_mode(sk); >+} >+ >+static u32 bbr_sndbuf_expand(struct sock *sk) >+{ >+ /* Provision 3 * cwnd since BBR may slow-start even during recovery. */ >+ return 3; >+} >+ >+/* In theory BBR does not need to undo the cwnd since it does not >+ * always reduce cwnd on losses (see bbr_main()). Keep it for now. >+ */ >+static u32 bbr_undo_cwnd(struct sock *sk) >+{ >+ return tcp_sk(sk)->snd_cwnd; >+} >+ >+/* Entering loss recovery, so save cwnd for when we exit or undo >recovery. */ >+static u32 bbr_ssthresh(struct sock *sk) >+{ >+ bbr_save_cwnd(sk); >+ return TCP_INFINITE_SSTHRESH; /* BBR does not use ssthresh */ >+} >+ >+static size_t bbr_get_info(struct sock *sk, u32 ext, int *attr, >+ union tcp_cc_info *info) >+{ >+ if (ext & (1 << (INET_DIAG_BBRINFO - 1)) || >+ ext & (1 << (INET_DIAG_VEGASINFO - 1))) { >+ struct tcp_sock *tp = tcp_sk(sk); >+ struct bbr *bbr = inet_csk_ca(sk); >+ u64 bw = bbr_bw(sk); >+ >+ bw = bw * tp->mss_cache * USEC_PER_SEC >> BW_SCALE; >+ memset(&info->bbr, 0, sizeof(info->bbr)); >+ info->bbr.bbr_bw_lo = (u32)bw; >+ info->bbr.bbr_bw_hi = (u32)(bw >> 32); >+ info->bbr.bbr_min_rtt = bbr->min_rtt_us; >+ info->bbr.bbr_pacing_gain = bbr->pacing_gain; >+ info->bbr.bbr_cwnd_gain = bbr->cwnd_gain; >+ *attr = INET_DIAG_BBRINFO; >+ return sizeof(info->bbr); >+ } >+ return 0; >+} >+ >+static void bbr_set_state(struct sock *sk, u8 new_state) >+{ >+ struct bbr *bbr = inet_csk_ca(sk); >+ >+ if (new_state == TCP_CA_Loss) { >+ struct rate_sample rs = { .losses = 1 }; >+ >+ bbr->prev_ca_state = TCP_CA_Loss; >+ bbr->full_bw = 0; >+ bbr->round_start = 1; /* treat RTO like end of a round */ >+ bbr_lt_bw_sampling(sk, &rs); >+ } >+} >+ >+static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = { >+ .flags = TCP_CONG_NON_RESTRICTED, >+ .name = "bbr", >+ .owner = THIS_MODULE, >+ .init = bbr_init, >+ .cong_control = bbr_main, >+ .sndbuf_expand = bbr_sndbuf_expand, >+ .undo_cwnd = bbr_undo_cwnd, >+ .cwnd_event = bbr_cwnd_event, >+ .ssthresh = bbr_ssthresh, >+ .tso_segs_goal = bbr_tso_segs_goal, >+ .get_info = bbr_get_info, >+ .set_state = bbr_set_state, >+}; >+ >+static int __init bbr_register(void) >+{ >+ BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE); >+ return tcp_register_congestion_control(&tcp_bbr_cong_ops); >+} >+ >+static void __exit bbr_unregister(void) >+{ >+ tcp_unregister_congestion_control(&tcp_bbr_cong_ops); >+} >+ >+module_init(bbr_register); >+module_exit(bbr_unregister); >+ >+MODULE_AUTHOR("Van Jacobson <v...@google.com>"); >+MODULE_AUTHOR("Neal Cardwell <ncardw...@google.com>"); >+MODULE_AUTHOR("Yuchung Cheng <ych...@google.com>"); >+MODULE_AUTHOR("Soheil Hassas Yeganeh <soh...@google.com>"); >+MODULE_LICENSE("Dual BSD/GPL"); >+MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)"); >-- >2.8.0.rc3.226.g39d4020 >
