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1174 lines
41 KiB
1174 lines
41 KiB
/* Bottleneck Bandwidth and RTT (BBR) congestion control |
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* |
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* BBR congestion control computes the sending rate based on the delivery |
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* rate (throughput) estimated from ACKs. In a nutshell: |
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* |
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* On each ACK, update our model of the network path: |
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* bottleneck_bandwidth = windowed_max(delivered / elapsed, 10 round trips) |
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* min_rtt = windowed_min(rtt, 10 seconds) |
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* pacing_rate = pacing_gain * bottleneck_bandwidth |
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* cwnd = max(cwnd_gain * bottleneck_bandwidth * min_rtt, 4) |
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* |
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* The core algorithm does not react directly to packet losses or delays, |
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* although BBR may adjust the size of next send per ACK when loss is |
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* observed, or adjust the sending rate if it estimates there is a |
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* traffic policer, in order to keep the drop rate reasonable. |
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* |
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* Here is a state transition diagram for BBR: |
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* |
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* | |
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* V |
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* +---> STARTUP ----+ |
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* | | | |
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* | V | |
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* | DRAIN ----+ |
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* | | | |
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* | V | |
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* +---> PROBE_BW ----+ |
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* | ^ | | |
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* | | | | |
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* | +----+ | |
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* | | |
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* +---- PROBE_RTT <--+ |
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* |
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* A BBR flow starts in STARTUP, and ramps up its sending rate quickly. |
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* When it estimates the pipe is full, it enters DRAIN to drain the queue. |
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* In steady state a BBR flow only uses PROBE_BW and PROBE_RTT. |
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* A long-lived BBR flow spends the vast majority of its time remaining |
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* (repeatedly) in PROBE_BW, fully probing and utilizing the pipe's bandwidth |
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* in a fair manner, with a small, bounded queue. *If* a flow has been |
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* continuously sending for the entire min_rtt window, and hasn't seen an RTT |
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* sample that matches or decreases its min_rtt estimate for 10 seconds, then |
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* it briefly enters PROBE_RTT to cut inflight to a minimum value to re-probe |
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* the path's two-way propagation delay (min_rtt). When exiting PROBE_RTT, if |
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* we estimated that we reached the full bw of the pipe then we enter PROBE_BW; |
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* otherwise we enter STARTUP to try to fill the pipe. |
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* |
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* BBR is described in detail in: |
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* "BBR: Congestion-Based Congestion Control", |
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* Neal Cardwell, Yuchung Cheng, C. Stephen Gunn, Soheil Hassas Yeganeh, |
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* Van Jacobson. ACM Queue, Vol. 14 No. 5, September-October 2016. |
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* |
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* There is a public e-mail list for discussing BBR development and testing: |
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* https://groups.google.com/forum/#!forum/bbr-dev |
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* |
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* NOTE: BBR might be used with the fq qdisc ("man tc-fq") with pacing enabled, |
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* otherwise TCP stack falls back to an internal pacing using one high |
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* resolution timer per TCP socket and may use more resources. |
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*/ |
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#include <linux/module.h> |
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#include <net/tcp.h> |
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#include <linux/inet_diag.h> |
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#include <linux/inet.h> |
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#include <linux/random.h> |
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#include <linux/win_minmax.h> |
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|
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/* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth |
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* estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps. |
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* This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32. |
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* Since the minimum window is >=4 packets, the lower bound isn't |
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* an issue. The upper bound isn't an issue with existing technologies. |
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*/ |
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#define BW_SCALE 24 |
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#define BW_UNIT (1 << BW_SCALE) |
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|
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#define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) */ |
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#define BBR_UNIT (1 << BBR_SCALE) |
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|
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/* BBR has the following modes for deciding how fast to send: */ |
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enum bbr_mode { |
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BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */ |
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BBR_DRAIN, /* drain any queue created during startup */ |
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BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */ |
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BBR_PROBE_RTT, /* cut inflight to min to probe min_rtt */ |
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}; |
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/* BBR congestion control block */ |
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struct bbr { |
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u32 min_rtt_us; /* min RTT in min_rtt_win_sec window */ |
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u32 min_rtt_stamp; /* timestamp of min_rtt_us */ |
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u32 probe_rtt_done_stamp; /* end time for BBR_PROBE_RTT mode */ |
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struct minmax bw; /* Max recent delivery rate in pkts/uS << 24 */ |
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u32 rtt_cnt; /* count of packet-timed rounds elapsed */ |
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u32 next_rtt_delivered; /* scb->tx.delivered at end of round */ |
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u64 cycle_mstamp; /* time of this cycle phase start */ |
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u32 mode:3, /* current bbr_mode in state machine */ |
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prev_ca_state:3, /* CA state on previous ACK */ |
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packet_conservation:1, /* use packet conservation? */ |
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round_start:1, /* start of packet-timed tx->ack round? */ |
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idle_restart:1, /* restarting after idle? */ |
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probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */ |
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unused:13, |
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lt_is_sampling:1, /* taking long-term ("LT") samples now? */ |
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lt_rtt_cnt:7, /* round trips in long-term interval */ |
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lt_use_bw:1; /* use lt_bw as our bw estimate? */ |
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u32 lt_bw; /* LT est delivery rate in pkts/uS << 24 */ |
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u32 lt_last_delivered; /* LT intvl start: tp->delivered */ |
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u32 lt_last_stamp; /* LT intvl start: tp->delivered_mstamp */ |
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u32 lt_last_lost; /* LT intvl start: tp->lost */ |
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u32 pacing_gain:10, /* current gain for setting pacing rate */ |
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cwnd_gain:10, /* current gain for setting cwnd */ |
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full_bw_reached:1, /* reached full bw in Startup? */ |
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full_bw_cnt:2, /* number of rounds without large bw gains */ |
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cycle_idx:3, /* current index in pacing_gain cycle array */ |
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has_seen_rtt:1, /* have we seen an RTT sample yet? */ |
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unused_b:5; |
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u32 prior_cwnd; /* prior cwnd upon entering loss recovery */ |
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u32 full_bw; /* recent bw, to estimate if pipe is full */ |
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|
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/* For tracking ACK aggregation: */ |
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u64 ack_epoch_mstamp; /* start of ACK sampling epoch */ |
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u16 extra_acked[2]; /* max excess data ACKed in epoch */ |
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u32 ack_epoch_acked:20, /* packets (S)ACKed in sampling epoch */ |
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extra_acked_win_rtts:5, /* age of extra_acked, in round trips */ |
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extra_acked_win_idx:1, /* current index in extra_acked array */ |
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unused_c:6; |
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}; |
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#define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */ |
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|
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/* Window length of bw filter (in rounds): */ |
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static const int bbr_bw_rtts = CYCLE_LEN + 2; |
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/* Window length of min_rtt filter (in sec): */ |
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static const u32 bbr_min_rtt_win_sec = 10; |
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/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */ |
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static const u32 bbr_probe_rtt_mode_ms = 200; |
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/* Skip TSO below the following bandwidth (bits/sec): */ |
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static const int bbr_min_tso_rate = 1200000; |
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/* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck. |
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* In order to help drive the network toward lower queues and low latency while |
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* maintaining high utilization, the average pacing rate aims to be slightly |
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* lower than the estimated bandwidth. This is an important aspect of the |
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* design. |
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*/ |
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static const int bbr_pacing_margin_percent = 1; |
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|
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/* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain |
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* that will allow a smoothly increasing pacing rate that will double each RTT |
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* and send the same number of packets per RTT that an un-paced, slow-starting |
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* Reno or CUBIC flow would: |
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*/ |
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static const int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1; |
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/* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain |
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* the queue created in BBR_STARTUP in a single round: |
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*/ |
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static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885; |
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/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */ |
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static const int bbr_cwnd_gain = BBR_UNIT * 2; |
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/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */ |
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static const int bbr_pacing_gain[] = { |
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BBR_UNIT * 5 / 4, /* probe for more available bw */ |
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BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */ |
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BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */ |
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BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */ |
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}; |
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/* Randomize the starting gain cycling phase over N phases: */ |
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static const u32 bbr_cycle_rand = 7; |
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/* Try to keep at least this many packets in flight, if things go smoothly. For |
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* smooth functioning, a sliding window protocol ACKing every other packet |
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* needs at least 4 packets in flight: |
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*/ |
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static const u32 bbr_cwnd_min_target = 4; |
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/* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */ |
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/* If bw has increased significantly (1.25x), there may be more bw available: */ |
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static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4; |
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/* But after 3 rounds w/o significant bw growth, estimate pipe is full: */ |
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static const u32 bbr_full_bw_cnt = 3; |
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|
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/* "long-term" ("LT") bandwidth estimator parameters... */ |
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/* The minimum number of rounds in an LT bw sampling interval: */ |
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static const u32 bbr_lt_intvl_min_rtts = 4; |
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/* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */ |
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static const u32 bbr_lt_loss_thresh = 50; |
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/* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */ |
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static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8; |
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/* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */ |
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static const u32 bbr_lt_bw_diff = 4000 / 8; |
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/* If we estimate we're policed, use lt_bw for this many round trips: */ |
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static const u32 bbr_lt_bw_max_rtts = 48; |
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/* Gain factor for adding extra_acked to target cwnd: */ |
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static const int bbr_extra_acked_gain = BBR_UNIT; |
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/* Window length of extra_acked window. */ |
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static const u32 bbr_extra_acked_win_rtts = 5; |
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/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */ |
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static const u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20; |
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/* Time period for clamping cwnd increment due to ack aggregation */ |
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static const u32 bbr_extra_acked_max_us = 100 * 1000; |
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static void bbr_check_probe_rtt_done(struct sock *sk); |
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/* Do we estimate that STARTUP filled the pipe? */ |
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static bool bbr_full_bw_reached(const struct sock *sk) |
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{ |
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const struct bbr *bbr = inet_csk_ca(sk); |
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return bbr->full_bw_reached; |
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} |
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/* Return the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */ |
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static u32 bbr_max_bw(const struct sock *sk) |
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{ |
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struct bbr *bbr = inet_csk_ca(sk); |
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return minmax_get(&bbr->bw); |
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} |
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/* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */ |
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static u32 bbr_bw(const struct sock *sk) |
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{ |
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struct bbr *bbr = inet_csk_ca(sk); |
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return bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk); |
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} |
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/* Return maximum extra acked in past k-2k round trips, |
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* where k = bbr_extra_acked_win_rtts. |
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*/ |
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static u16 bbr_extra_acked(const struct sock *sk) |
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{ |
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struct bbr *bbr = inet_csk_ca(sk); |
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return max(bbr->extra_acked[0], bbr->extra_acked[1]); |
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} |
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/* Return rate in bytes per second, optionally with a gain. |
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* The order here is chosen carefully to avoid overflow of u64. This should |
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* work for input rates of up to 2.9Tbit/sec and gain of 2.89x. |
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*/ |
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static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain) |
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{ |
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unsigned int mss = tcp_sk(sk)->mss_cache; |
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rate *= mss; |
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rate *= gain; |
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rate >>= BBR_SCALE; |
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rate *= USEC_PER_SEC / 100 * (100 - bbr_pacing_margin_percent); |
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return rate >> BW_SCALE; |
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} |
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/* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */ |
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static unsigned long bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain) |
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{ |
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u64 rate = bw; |
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rate = bbr_rate_bytes_per_sec(sk, rate, gain); |
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rate = min_t(u64, rate, sk->sk_max_pacing_rate); |
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return rate; |
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} |
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/* Initialize pacing rate to: high_gain * init_cwnd / RTT. */ |
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static void bbr_init_pacing_rate_from_rtt(struct sock *sk) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct bbr *bbr = inet_csk_ca(sk); |
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u64 bw; |
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u32 rtt_us; |
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if (tp->srtt_us) { /* any RTT sample yet? */ |
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rtt_us = max(tp->srtt_us >> 3, 1U); |
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bbr->has_seen_rtt = 1; |
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} else { /* no RTT sample yet */ |
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rtt_us = USEC_PER_MSEC; /* use nominal default RTT */ |
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} |
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bw = (u64)tp->snd_cwnd * BW_UNIT; |
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do_div(bw, rtt_us); |
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sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain); |
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} |
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/* Pace using current bw estimate and a gain factor. */ |
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static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct bbr *bbr = inet_csk_ca(sk); |
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unsigned long rate = bbr_bw_to_pacing_rate(sk, bw, gain); |
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if (unlikely(!bbr->has_seen_rtt && tp->srtt_us)) |
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bbr_init_pacing_rate_from_rtt(sk); |
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if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate) |
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sk->sk_pacing_rate = rate; |
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} |
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/* override sysctl_tcp_min_tso_segs */ |
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static u32 bbr_min_tso_segs(struct sock *sk) |
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{ |
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return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2; |
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} |
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static u32 bbr_tso_segs_goal(struct sock *sk) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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u32 segs, bytes; |
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/* Sort of tcp_tso_autosize() but ignoring |
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* driver provided sk_gso_max_size. |
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*/ |
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bytes = min_t(unsigned long, |
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sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift), |
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GSO_MAX_SIZE - 1 - MAX_TCP_HEADER); |
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segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk)); |
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return min(segs, 0x7FU); |
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} |
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/* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */ |
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static void bbr_save_cwnd(struct sock *sk) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct bbr *bbr = inet_csk_ca(sk); |
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if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT) |
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bbr->prior_cwnd = tp->snd_cwnd; /* this cwnd is good enough */ |
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else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */ |
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bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd); |
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} |
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static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct bbr *bbr = inet_csk_ca(sk); |
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if (event == CA_EVENT_TX_START && tp->app_limited) { |
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bbr->idle_restart = 1; |
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bbr->ack_epoch_mstamp = tp->tcp_mstamp; |
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bbr->ack_epoch_acked = 0; |
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/* Avoid pointless buffer overflows: pace at est. bw if we don't |
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* need more speed (we're restarting from idle and app-limited). |
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*/ |
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if (bbr->mode == BBR_PROBE_BW) |
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bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT); |
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else if (bbr->mode == BBR_PROBE_RTT) |
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bbr_check_probe_rtt_done(sk); |
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} |
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} |
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/* Calculate bdp based on min RTT and the estimated bottleneck bandwidth: |
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* |
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* bdp = ceil(bw * min_rtt * gain) |
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* |
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* The key factor, gain, controls the amount of queue. While a small gain |
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* builds a smaller queue, it becomes more vulnerable to noise in RTT |
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* measurements (e.g., delayed ACKs or other ACK compression effects). This |
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* noise may cause BBR to under-estimate the rate. |
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*/ |
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static u32 bbr_bdp(struct sock *sk, u32 bw, int gain) |
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{ |
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struct bbr *bbr = inet_csk_ca(sk); |
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u32 bdp; |
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u64 w; |
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/* If we've never had a valid RTT sample, cap cwnd at the initial |
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* default. This should only happen when the connection is not using TCP |
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* timestamps and has retransmitted all of the SYN/SYNACK/data packets |
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* ACKed so far. In this case, an RTO can cut cwnd to 1, in which |
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* case we need to slow-start up toward something safe: TCP_INIT_CWND. |
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*/ |
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if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */ |
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return TCP_INIT_CWND; /* be safe: cap at default initial cwnd*/ |
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w = (u64)bw * bbr->min_rtt_us; |
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|
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/* Apply a gain to the given value, remove the BW_SCALE shift, and |
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* round the value up to avoid a negative feedback loop. |
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*/ |
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bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; |
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return bdp; |
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} |
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|
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/* To achieve full performance in high-speed paths, we budget enough cwnd to |
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* fit full-sized skbs in-flight on both end hosts to fully utilize the path: |
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* - one skb in sending host Qdisc, |
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* - one skb in sending host TSO/GSO engine |
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* - one skb being received by receiver host LRO/GRO/delayed-ACK engine |
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* Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because |
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* in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets, |
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* which allows 2 outstanding 2-packet sequences, to try to keep pipe |
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* full even with ACK-every-other-packet delayed ACKs. |
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*/ |
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static u32 bbr_quantization_budget(struct sock *sk, u32 cwnd) |
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{ |
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struct bbr *bbr = inet_csk_ca(sk); |
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/* Allow enough full-sized skbs in flight to utilize end systems. */ |
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cwnd += 3 * bbr_tso_segs_goal(sk); |
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|
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/* Reduce delayed ACKs by rounding up cwnd to the next even number. */ |
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cwnd = (cwnd + 1) & ~1U; |
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/* Ensure gain cycling gets inflight above BDP even for small BDPs. */ |
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if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == 0) |
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cwnd += 2; |
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return cwnd; |
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} |
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/* Find inflight based on min RTT and the estimated bottleneck bandwidth. */ |
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static u32 bbr_inflight(struct sock *sk, u32 bw, int gain) |
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{ |
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u32 inflight; |
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inflight = bbr_bdp(sk, bw, gain); |
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inflight = bbr_quantization_budget(sk, inflight); |
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return inflight; |
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} |
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/* With pacing at lower layers, there's often less data "in the network" than |
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* "in flight". With TSQ and departure time pacing at lower layers (e.g. fq), |
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* we often have several skbs queued in the pacing layer with a pre-scheduled |
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* earliest departure time (EDT). BBR adapts its pacing rate based on the |
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* inflight level that it estimates has already been "baked in" by previous |
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* departure time decisions. We calculate a rough estimate of the number of our |
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* packets that might be in the network at the earliest departure time for the |
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* next skb scheduled: |
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* in_network_at_edt = inflight_at_edt - (EDT - now) * bw |
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* If we're increasing inflight, then we want to know if the transmit of the |
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* EDT skb will push inflight above the target, so inflight_at_edt includes |
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* bbr_tso_segs_goal() from the skb departing at EDT. If decreasing inflight, |
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* then estimate if inflight will sink too low just before the EDT transmit. |
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*/ |
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static u32 bbr_packets_in_net_at_edt(struct sock *sk, u32 inflight_now) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct bbr *bbr = inet_csk_ca(sk); |
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u64 now_ns, edt_ns, interval_us; |
|
u32 interval_delivered, inflight_at_edt; |
|
|
|
now_ns = tp->tcp_clock_cache; |
|
edt_ns = max(tp->tcp_wstamp_ns, now_ns); |
|
interval_us = div_u64(edt_ns - now_ns, NSEC_PER_USEC); |
|
interval_delivered = (u64)bbr_bw(sk) * interval_us >> BW_SCALE; |
|
inflight_at_edt = inflight_now; |
|
if (bbr->pacing_gain > BBR_UNIT) /* increasing inflight */ |
|
inflight_at_edt += bbr_tso_segs_goal(sk); /* include EDT skb */ |
|
if (interval_delivered >= inflight_at_edt) |
|
return 0; |
|
return inflight_at_edt - interval_delivered; |
|
} |
|
|
|
/* Find the cwnd increment based on estimate of ack aggregation */ |
|
static u32 bbr_ack_aggregation_cwnd(struct sock *sk) |
|
{ |
|
u32 max_aggr_cwnd, aggr_cwnd = 0; |
|
|
|
if (bbr_extra_acked_gain && bbr_full_bw_reached(sk)) { |
|
max_aggr_cwnd = ((u64)bbr_bw(sk) * bbr_extra_acked_max_us) |
|
/ BW_UNIT; |
|
aggr_cwnd = (bbr_extra_acked_gain * bbr_extra_acked(sk)) |
|
>> BBR_SCALE; |
|
aggr_cwnd = min(aggr_cwnd, max_aggr_cwnd); |
|
} |
|
|
|
return aggr_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. */ |
|
cwnd = max(cwnd, bbr->prior_cwnd); |
|
bbr->packet_conservation = 0; |
|
} |
|
bbr->prev_ca_state = state; |
|
|
|
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 = tp->snd_cwnd, target_cwnd = 0; |
|
|
|
if (!acked) |
|
goto done; /* no packet fully ACKed; just apply caps */ |
|
|
|
if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd)) |
|
goto done; |
|
|
|
target_cwnd = bbr_bdp(sk, bw, gain); |
|
|
|
/* Increment the cwnd to account for excess ACKed data that seems |
|
* due to aggregation (of data and/or ACKs) visible in the ACK stream. |
|
*/ |
|
target_cwnd += bbr_ack_aggregation_cwnd(sk); |
|
target_cwnd = bbr_quantization_budget(sk, target_cwnd); |
|
|
|
/* If we're below target cwnd, slow start cwnd toward target cwnd. */ |
|
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 = |
|
tcp_stamp_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 = bbr_packets_in_net_at_edt(sk, rs->prior_in_flight); |
|
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_inflight(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_inflight(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; |
|
} |
|
|
|
/* 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_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; |
|
} |
|
|
|
static void bbr_reset_probe_bw_mode(struct sock *sk) |
|
{ |
|
struct bbr *bbr = inet_csk_ca(sk); |
|
|
|
bbr->mode = BBR_PROBE_BW; |
|
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 = div_u64(tp->delivered_mstamp, USEC_PER_MSEC); |
|
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; |
|
u32 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 = div_u64(tp->delivered_mstamp, USEC_PER_MSEC) - bbr->lt_last_stamp; |
|
if ((s32)t < 1) |
|
return; /* interval is less than one ms, so wait */ |
|
/* Check if can multiply without overflow */ |
|
if (t >= ~0U / USEC_PER_MSEC) { |
|
bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */ |
|
return; |
|
} |
|
t *= USEC_PER_MSEC; |
|
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 = div64_long((u64)rs->delivered * BW_UNIT, 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); |
|
} |
|
} |
|
|
|
/* Estimates the windowed max degree of ack aggregation. |
|
* This is used to provision extra in-flight data to keep sending during |
|
* inter-ACK silences. |
|
* |
|
* Degree of ack aggregation is estimated as extra data acked beyond expected. |
|
* |
|
* max_extra_acked = "maximum recent excess data ACKed beyond max_bw * interval" |
|
* cwnd += max_extra_acked |
|
* |
|
* Max extra_acked is clamped by cwnd and bw * bbr_extra_acked_max_us (100 ms). |
|
* Max filter is an approximate sliding window of 5-10 (packet timed) round |
|
* trips. |
|
*/ |
|
static void bbr_update_ack_aggregation(struct sock *sk, |
|
const struct rate_sample *rs) |
|
{ |
|
u32 epoch_us, expected_acked, extra_acked; |
|
struct bbr *bbr = inet_csk_ca(sk); |
|
struct tcp_sock *tp = tcp_sk(sk); |
|
|
|
if (!bbr_extra_acked_gain || rs->acked_sacked <= 0 || |
|
rs->delivered < 0 || rs->interval_us <= 0) |
|
return; |
|
|
|
if (bbr->round_start) { |
|
bbr->extra_acked_win_rtts = min(0x1F, |
|
bbr->extra_acked_win_rtts + 1); |
|
if (bbr->extra_acked_win_rtts >= bbr_extra_acked_win_rtts) { |
|
bbr->extra_acked_win_rtts = 0; |
|
bbr->extra_acked_win_idx = bbr->extra_acked_win_idx ? |
|
0 : 1; |
|
bbr->extra_acked[bbr->extra_acked_win_idx] = 0; |
|
} |
|
} |
|
|
|
/* Compute how many packets we expected to be delivered over epoch. */ |
|
epoch_us = tcp_stamp_us_delta(tp->delivered_mstamp, |
|
bbr->ack_epoch_mstamp); |
|
expected_acked = ((u64)bbr_bw(sk) * epoch_us) / BW_UNIT; |
|
|
|
/* Reset the aggregation epoch if ACK rate is below expected rate or |
|
* significantly large no. of ack received since epoch (potentially |
|
* quite old epoch). |
|
*/ |
|
if (bbr->ack_epoch_acked <= expected_acked || |
|
(bbr->ack_epoch_acked + rs->acked_sacked >= |
|
bbr_ack_epoch_acked_reset_thresh)) { |
|
bbr->ack_epoch_acked = 0; |
|
bbr->ack_epoch_mstamp = tp->delivered_mstamp; |
|
expected_acked = 0; |
|
} |
|
|
|
/* Compute excess data delivered, beyond what was expected. */ |
|
bbr->ack_epoch_acked = min_t(u32, 0xFFFFF, |
|
bbr->ack_epoch_acked + rs->acked_sacked); |
|
extra_acked = bbr->ack_epoch_acked - expected_acked; |
|
extra_acked = min(extra_acked, tp->snd_cwnd); |
|
if (extra_acked > bbr->extra_acked[bbr->extra_acked_win_idx]) |
|
bbr->extra_acked[bbr->extra_acked_win_idx] = extra_acked; |
|
} |
|
|
|
/* 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; |
|
bbr->full_bw_reached = bbr->full_bw_cnt >= 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 */ |
|
tcp_sk(sk)->snd_ssthresh = |
|
bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT); |
|
} /* fall through to check if in-flight is already small: */ |
|
if (bbr->mode == BBR_DRAIN && |
|
bbr_packets_in_net_at_edt(sk, tcp_packets_in_flight(tcp_sk(sk))) <= |
|
bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT)) |
|
bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ |
|
} |
|
|
|
static void bbr_check_probe_rtt_done(struct sock *sk) |
|
{ |
|
struct tcp_sock *tp = tcp_sk(sk); |
|
struct bbr *bbr = inet_csk_ca(sk); |
|
|
|
if (!(bbr->probe_rtt_done_stamp && |
|
after(tcp_jiffies32, bbr->probe_rtt_done_stamp))) |
|
return; |
|
|
|
bbr->min_rtt_stamp = tcp_jiffies32; /* wait a while until PROBE_RTT */ |
|
tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd); |
|
bbr_reset_mode(sk); |
|
} |
|
|
|
/* 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_jiffies32, |
|
bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ); |
|
if (rs->rtt_us >= 0 && |
|
(rs->rtt_us < bbr->min_rtt_us || |
|
(filter_expired && !rs->is_ack_delayed))) { |
|
bbr->min_rtt_us = rs->rtt_us; |
|
bbr->min_rtt_stamp = tcp_jiffies32; |
|
} |
|
|
|
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_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_jiffies32 + |
|
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) |
|
bbr_check_probe_rtt_done(sk); |
|
} |
|
} |
|
/* Restart after idle ends only once we process a new S/ACK for data */ |
|
if (rs->delivered > 0) |
|
bbr->idle_restart = 0; |
|
} |
|
|
|
static void bbr_update_gains(struct sock *sk) |
|
{ |
|
struct bbr *bbr = inet_csk_ca(sk); |
|
|
|
switch (bbr->mode) { |
|
case BBR_STARTUP: |
|
bbr->pacing_gain = bbr_high_gain; |
|
bbr->cwnd_gain = bbr_high_gain; |
|
break; |
|
case BBR_DRAIN: |
|
bbr->pacing_gain = bbr_drain_gain; /* slow, to drain */ |
|
bbr->cwnd_gain = bbr_high_gain; /* keep cwnd */ |
|
break; |
|
case BBR_PROBE_BW: |
|
bbr->pacing_gain = (bbr->lt_use_bw ? |
|
BBR_UNIT : |
|
bbr_pacing_gain[bbr->cycle_idx]); |
|
bbr->cwnd_gain = bbr_cwnd_gain; |
|
break; |
|
case BBR_PROBE_RTT: |
|
bbr->pacing_gain = BBR_UNIT; |
|
bbr->cwnd_gain = BBR_UNIT; |
|
break; |
|
default: |
|
WARN_ONCE(1, "BBR bad mode: %u\n", bbr->mode); |
|
break; |
|
} |
|
} |
|
|
|
static void bbr_update_model(struct sock *sk, const struct rate_sample *rs) |
|
{ |
|
bbr_update_bw(sk, rs); |
|
bbr_update_ack_aggregation(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); |
|
bbr_update_gains(sk); |
|
} |
|
|
|
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_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); |
|
|
|
bbr->prior_cwnd = 0; |
|
tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; |
|
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_jiffies32; |
|
|
|
minmax_reset(&bbr->bw, bbr->rtt_cnt, 0); /* init max bw to 0 */ |
|
|
|
bbr->has_seen_rtt = 0; |
|
bbr_init_pacing_rate_from_rtt(sk); |
|
|
|
bbr->round_start = 0; |
|
bbr->idle_restart = 0; |
|
bbr->full_bw_reached = 0; |
|
bbr->full_bw = 0; |
|
bbr->full_bw_cnt = 0; |
|
bbr->cycle_mstamp = 0; |
|
bbr->cycle_idx = 0; |
|
bbr_reset_lt_bw_sampling(sk); |
|
bbr_reset_startup_mode(sk); |
|
|
|
bbr->ack_epoch_mstamp = tp->tcp_mstamp; |
|
bbr->ack_epoch_acked = 0; |
|
bbr->extra_acked_win_rtts = 0; |
|
bbr->extra_acked_win_idx = 0; |
|
bbr->extra_acked[0] = 0; |
|
bbr->extra_acked[1] = 0; |
|
|
|
cmpxchg(&sk->sk_pacing_status, SK_PACING_NONE, SK_PACING_NEEDED); |
|
} |
|
|
|
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) |
|
{ |
|
struct bbr *bbr = inet_csk_ca(sk); |
|
|
|
bbr->full_bw = 0; /* spurious slow-down; reset full pipe detection */ |
|
bbr->full_bw_cnt = 0; |
|
bbr_reset_lt_bw_sampling(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_sk(sk)->snd_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, |
|
.min_tso_segs = bbr_min_tso_segs, |
|
.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 <[email protected]>"); |
|
MODULE_AUTHOR("Neal Cardwell <[email protected]>"); |
|
MODULE_AUTHOR("Yuchung Cheng <[email protected]>"); |
|
MODULE_AUTHOR("Soheil Hassas Yeganeh <[email protected]>"); |
|
MODULE_LICENSE("Dual BSD/GPL"); |
|
MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");
|
|
|