From 81d1612bc7b1d0b8f92b460933d32ae2cc30f839 Mon Sep 17 00:00:00 2001 From: QiuSimons <45143996+QiuSimons@users.noreply.github.com> Date: Tue, 25 Feb 2020 16:05:39 +0800 Subject: [PATCH] tcp_bbr: adapt cwnd based on ack aggregation estimation (#35) --- ...-based-on-ack-aggregation-estimation.patch | 458 ++++++++++++++++++ 1 file changed, 458 insertions(+) create mode 100644 target/linux/generic/pending-4.14/607-tcp_bbr-adapt-cwnd-based-on-ack-aggregation-estimation.patch diff --git a/target/linux/generic/pending-4.14/607-tcp_bbr-adapt-cwnd-based-on-ack-aggregation-estimation.patch b/target/linux/generic/pending-4.14/607-tcp_bbr-adapt-cwnd-based-on-ack-aggregation-estimation.patch new file mode 100644 index 0000000000..fb6bd77b07 --- /dev/null +++ b/target/linux/generic/pending-4.14/607-tcp_bbr-adapt-cwnd-based-on-ack-aggregation-estimation.patch @@ -0,0 +1,458 @@ +From 232aa8ec3ed979d4716891540c03a806ecab0c37 Mon Sep 17 00:00:00 2001 +From: Priyaranjan Jha +Date: Wed, 23 Jan 2019 12:04:53 -0800 +Subject: tcp_bbr: refactor bbr_target_cwnd() for general inflight provisioning + +Because bbr_target_cwnd() is really a general-purpose BBR helper for +computing some volume of inflight data as a function of the estimated +BDP, refactor it into following helper functions: +- bbr_bdp() +- bbr_quantization_budget() +- bbr_inflight() + +Signed-off-by: Priyaranjan Jha +Signed-off-by: Neal Cardwell +Signed-off-by: Yuchung Cheng +Signed-off-by: David S. Miller +--- +diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c +--- a/net/ipv4/tcp_bbr.c ++++ b/net/ipv4/tcp_bbr.c +@@ -97,10 +97,11 @@ + 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? */ ++ cycle_len:4, /* phases in this PROBE_BW gain cycle */ + 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, ++ unused:8, + 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? */ +@@ -117,6 +118,14 @@ + unused_b:5; + u32 prior_cwnd; /* prior cwnd upon entering loss recovery */ + u32 full_bw; /* recent bw, to estimate if pipe is full */ ++ ++ /* For tracking ACK aggregation: */ ++ u64 ack_epoch_mstamp; /* start of ACK sampling epoch */ ++ u16 extra_acked[2]; /* max excess data ACKed in epoch */ ++ u32 ack_epoch_acked:20, /* packets (S)ACKed in sampling epoch */ ++ extra_acked_win_rtts:5, /* age of extra_acked, in round trips */ ++ extra_acked_win_idx:1, /* current index in extra_acked array */ ++ unused1:6; + }; + + #define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */ +@@ -143,6 +152,11 @@ + /* 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: */ ++enum bbr_pacing_gain_phase { ++ BBR_BW_PROBE_UP = 0, ++ BBR_BW_PROBE_DOWN = 1, ++ BBR_BW_PROBE_CRUISE = 2, ++}; + 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 */ +@@ -176,6 +190,25 @@ + /* If we estimate we're policed, use lt_bw for this many round trips: */ + static const u32 bbr_lt_bw_max_rtts = 48; + ++/* Gain factor for adding extra_acked to target cwnd: */ ++static int bbr_extra_acked_gain = BBR_UNIT; ++/* Window length of extra_acked window. Max allowed val is 31. */ ++static const u32 bbr_extra_acked_win_rtts = 10; ++/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */ ++static const u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20; ++/* Time period for clamping cwnd increment due to ack aggregation */ ++static const u32 bbr_extra_acked_max_us = 100 * 1000; ++ ++/* Each cycle, try to hold sub-unity gain until inflight <= BDP. */ ++static bool bbr_drain_to_target = true; /* default: enabled */ ++ ++extern bool tcp_snd_wnd_test(const struct tcp_sock *tp, ++ const struct sk_buff *skb, ++ unsigned int cur_mss); ++ ++module_param_named(extra_acked_gain, bbr_extra_acked_gain, int, 0664); ++module_param_named(drain_to_target, bbr_drain_to_target, bool, 0664); ++ + /* Do we estimate that STARTUP filled the pipe? */ + static bool bbr_full_bw_reached(const struct sock *sk) + { +@@ -200,6 +233,16 @@ + return bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk); + } + ++/* Return maximum extra acked in past k-2k round trips, ++ * where k = bbr_extra_acked_win_rtts. ++ */ ++static u16 bbr_extra_acked(const struct sock *sk) ++{ ++ struct bbr *bbr = inet_csk_ca(sk); ++ ++ return max(bbr->extra_acked[0], bbr->extra_acked[1]); ++} ++ + /* 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. +@@ -299,6 +342,8 @@ + + if (event == CA_EVENT_TX_START && tp->app_limited) { + bbr->idle_restart = 1; ++ bbr->ack_epoch_mstamp = tp->tcp_mstamp; ++ bbr->ack_epoch_acked = 0; + /* Avoid pointless buffer overflows: pace at est. bw if we don't + * need more speed (we're restarting from idle and app-limited). + */ +@@ -307,30 +352,19 @@ + } + } + +-/* Find target cwnd. Right-size the cwnd based on min RTT and the +- * estimated bottleneck bandwidth: ++/* Calculate bdp based on min RTT and the estimated bottleneck bandwidth: + * +- * cwnd = bw * min_rtt * gain = BDP * gain ++ * bdp = bw * min_rtt * 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) ++static u32 bbr_bdp(struct sock *sk, u32 bw, int gain) + { + struct bbr *bbr = inet_csk_ca(sk); +- u32 cwnd; ++ u32 bdp; + u64 w; + + /* If we've never had a valid RTT sample, cap cwnd at the initial +@@ -345,8 +379,24 @@ + 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; ++ bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; + ++ return bdp; ++} ++ ++/* 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_quantization_budget(struct sock *sk, u32 cwnd, int gain) ++{ ++ struct bbr *bbr = inet_csk_ca(sk); + /* Allow enough full-sized skbs in flight to utilize end systems. */ + cwnd += 3 * bbr->tso_segs_goal; + +@@ -360,6 +410,33 @@ + return cwnd; + } + ++/* Find inflight based on min RTT and the estimated bottleneck bandwidth. */ ++static u32 bbr_inflight(struct sock *sk, u32 bw, int gain) ++{ ++ u32 inflight; ++ ++ inflight = bbr_bdp(sk, bw, gain); ++ inflight = bbr_quantization_budget(sk, inflight, gain); ++ ++ return inflight; ++} ++ ++/* 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. +@@ -427,7 +504,14 @@ + goto done; + + /* If we're below target cwnd, slow start cwnd toward target cwnd. */ +- target_cwnd = bbr_target_cwnd(sk, bw, gain); ++ 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, 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) +@@ -468,14 +552,80 @@ + 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)); ++ 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_target_cwnd(sk, bw, BBR_UNIT); ++ inflight <= bbr_inflight(sk, bw, BBR_UNIT); ++} ++ ++static void bbr_set_cycle_idx(struct sock *sk, int cycle_idx) ++{ ++ struct bbr *bbr = inet_csk_ca(sk); ++ ++ bbr->cycle_idx = cycle_idx; ++ bbr->pacing_gain = bbr->lt_use_bw ? ++ BBR_UNIT : bbr_pacing_gain[bbr->cycle_idx]; ++} ++ ++static void bbr_drain_to_target_cycling(struct sock *sk, ++ const struct rate_sample *rs) ++{ ++ struct tcp_sock *tp = tcp_sk(sk); ++ struct bbr *bbr = inet_csk_ca(sk); ++ u32 elapsed_us = ++ tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp); ++ u32 inflight, bw; ++ ++ if (bbr->mode != BBR_PROBE_BW) ++ return; ++ ++ /* Always need to probe for bw before we forget good bw estimate. */ ++ if (elapsed_us > bbr->cycle_len * bbr->min_rtt_us) { ++ /* Start a new PROBE_BW probing cycle of [2 to 8] x min_rtt. */ ++ bbr->cycle_mstamp = tp->delivered_mstamp; ++ bbr->cycle_len = CYCLE_LEN - prandom_u32_max(bbr_cycle_rand); ++ bbr_set_cycle_idx(sk, BBR_BW_PROBE_UP); /* probe bandwidth */ ++ return; ++ } ++ ++ /* 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; ++ ++ inflight = rs->prior_in_flight; /* what was in-flight before ACK? */ ++ bw = bbr_max_bw(sk); ++ ++ /* 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. ++ */ ++ if (bbr->pacing_gain < BBR_UNIT) { ++ if (inflight <= bbr_inflight(sk, bw, BBR_UNIT)) ++ bbr_set_cycle_idx(sk, BBR_BW_PROBE_CRUISE); /* cruise */ ++ return; ++ } ++ ++ /* 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. Similarly we exit ++ * if we were prevented by app/recv-win from reaching the target. ++ */ ++ if (elapsed_us > bbr->min_rtt_us && ++ (inflight >= bbr_inflight(sk, bw, bbr->pacing_gain) || ++ rs->losses || /* perhaps pacing_gain*BDP won't fit */ ++ rs->is_app_limited || /* previously app-limited */ ++ !tcp_send_head(sk) || /* currently app/rwin-limited */ ++ !tcp_snd_wnd_test(tp, tcp_send_head(sk), tp->mss_cache))) { ++ bbr_set_cycle_idx(sk, BBR_BW_PROBE_DOWN); /* drain queue */ ++ return; ++ } + } + + static void bbr_advance_cycle_phase(struct sock *sk) +@@ -495,6 +645,11 @@ + { + struct bbr *bbr = inet_csk_ca(sk); + ++ if (bbr_drain_to_target) { ++ bbr_drain_to_target_cycling(sk, rs); ++ return; ++ } ++ + if (bbr->mode == BBR_PROBE_BW && bbr_is_next_cycle_phase(sk, rs)) + bbr_advance_cycle_phase(sk); + } +@@ -698,6 +853,67 @@ + } + } + ++/* 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 10-20 (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(0xFFFFFU, ++ 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 +@@ -733,11 +949,12 @@ + 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 */ ++ 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 && + tcp_packets_in_flight(tcp_sk(sk)) <= +- bbr_target_cwnd(sk, bbr_max_bw(sk), BBR_UNIT)) ++ bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT)) + bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */ + } + +@@ -814,6 +1031,7 @@ + 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); +@@ -863,9 +1081,17 @@ + bbr->full_bw_cnt = 0; + bbr->cycle_mstamp = 0; + bbr->cycle_idx = 0; ++ bbr->cycle_len = 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); + } + +@@ -948,7 +1174,7 @@ + + static int __init bbr_register(void) + { +- BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE); ++/* BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);*/ + return tcp_register_congestion_control(&tcp_bbr_cong_ops); + } + +diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c +--- a/net/ipv4/tcp_output.c ++++ b/net/ipv4/tcp_output.c +@@ -1824,8 +1824,7 @@ + } + + /* Does at least the first segment of SKB fit into the send window? */ +-static bool tcp_snd_wnd_test(const struct tcp_sock *tp, +- const struct sk_buff *skb, ++bool tcp_snd_wnd_test(const struct tcp_sock *tp, const struct sk_buff *skb, + unsigned int cur_mss) + { + u32 end_seq = TCP_SKB_CB(skb)->end_seq; +@@ -1835,6 +1834,7 @@ + + return !after(end_seq, tcp_wnd_end(tp)); + } ++EXPORT_SYMBOL(tcp_snd_wnd_test); + + /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet + * which is put after SKB on the list. It is very much like +