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Diffstat (limited to 'net/ipv4/tcp_bbr.c')
-rw-r--r--net/ipv4/tcp_bbr.c90
1 files changed, 72 insertions, 18 deletions
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 02ff2dde9609..9277abdd822a 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -128,6 +128,9 @@ 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;
+/* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck. */
+static const int bbr_pacing_margin_percent = 1;
+
/* 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
@@ -208,17 +211,15 @@ static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain)
{
unsigned int mss = tcp_sk(sk)->mss_cache;
- if (!tcp_needs_internal_pacing(sk))
- mss = tcp_mss_to_mtu(sk, mss);
rate *= mss;
rate *= gain;
rate >>= BBR_SCALE;
- rate *= USEC_PER_SEC;
+ rate *= USEC_PER_SEC / 100 * (100 - bbr_pacing_margin_percent);
return rate >> BW_SCALE;
}
/* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */
-static u32 bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)
+static unsigned long bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)
{
u64 rate = bw;
@@ -257,7 +258,7 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
- u32 rate = bbr_bw_to_pacing_rate(sk, bw, gain);
+ unsigned long rate = bbr_bw_to_pacing_rate(sk, bw, gain);
if (unlikely(!bbr->has_seen_rtt && tp->srtt_us))
bbr_init_pacing_rate_from_rtt(sk);
@@ -279,7 +280,7 @@ static u32 bbr_tso_segs_goal(struct sock *sk)
/* Sort of tcp_tso_autosize() but ignoring
* driver provided sk_gso_max_size.
*/
- bytes = min_t(u32, sk->sk_pacing_rate >> sk->sk_pacing_shift,
+ bytes = min_t(unsigned long, sk->sk_pacing_rate >> sk->sk_pacing_shift,
GSO_MAX_SIZE - 1 - MAX_TCP_HEADER);
segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk));
@@ -368,6 +369,39 @@ static u32 bbr_target_cwnd(struct sock *sk, u32 bw, int gain)
return cwnd;
}
+/* With pacing at lower layers, there's often less data "in the network" than
+ * "in flight". With TSQ and departure time pacing at lower layers (e.g. fq),
+ * we often have several skbs queued in the pacing layer with a pre-scheduled
+ * earliest departure time (EDT). BBR adapts its pacing rate based on the
+ * inflight level that it estimates has already been "baked in" by previous
+ * departure time decisions. We calculate a rough estimate of the number of our
+ * packets that might be in the network at the earliest departure time for the
+ * next skb scheduled:
+ * in_network_at_edt = inflight_at_edt - (EDT - now) * bw
+ * If we're increasing inflight, then we want to know if the transmit of the
+ * EDT skb will push inflight above the target, so inflight_at_edt includes
+ * bbr_tso_segs_goal() from the skb departing at EDT. If decreasing inflight,
+ * then estimate if inflight will sink too low just before the EDT transmit.
+ */
+static u32 bbr_packets_in_net_at_edt(struct sock *sk, u32 inflight_now)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct bbr *bbr = inet_csk_ca(sk);
+ 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;
+}
+
/* 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.
@@ -459,7 +493,7 @@ static bool bbr_is_next_cycle_phase(struct sock *sk,
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? */
+ 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
@@ -487,8 +521,6 @@ static void bbr_advance_cycle_phase(struct sock *sk)
bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1);
bbr->cycle_mstamp = tp->delivered_mstamp;
- bbr->pacing_gain = bbr->lt_use_bw ? BBR_UNIT :
- bbr_pacing_gain[bbr->cycle_idx];
}
/* Gain cycling: cycle pacing gain to converge to fair share of available bw. */
@@ -506,8 +538,6 @@ 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)
@@ -515,8 +545,6 @@ 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 */
}
@@ -734,13 +762,11 @@ static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs)
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_target_cwnd(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_packets_in_net_at_edt(sk, 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 */
}
@@ -797,8 +823,6 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
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;
}
@@ -826,6 +850,35 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
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);
@@ -833,6 +886,7 @@ static void bbr_update_model(struct sock *sk, const struct rate_sample *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)
generated by cgit v1.2.3 (git 2.39.0) at 2025-01-09 01:12:57 +0300