From d1e59a46973719e458bec78d00dd767d7a7ba71f Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 23 Mar 2026 23:49:20 +0000 Subject: tcp: add cwnd_event_tx_start to tcp_congestion_ops (tcp_congestion_ops)->cwnd_event() is called very often, with @event oscillating between CA_EVENT_TX_START and other values. This is not branch prediction friendly. Provide a new cwnd_event_tx_start pointer dedicated for CA_EVENT_TX_START. Both BBR and CUBIC benefit from this change, since they only care about CA_EVENT_TX_START. No change in kernel size: $ scripts/bloat-o-meter -t vmlinux.0 vmlinux add/remove: 4/4 grow/shrink: 3/1 up/down: 564/-568 (-4) Function old new delta bbr_cwnd_event_tx_start - 450 +450 cubictcp_cwnd_event_tx_start - 70 +70 __pfx_cubictcp_cwnd_event_tx_start - 16 +16 __pfx_bbr_cwnd_event_tx_start - 16 +16 tcp_unregister_congestion_control 93 99 +6 tcp_update_congestion_control 518 521 +3 tcp_register_congestion_control 422 425 +3 __tcp_transmit_skb 3308 3306 -2 __pfx_cubictcp_cwnd_event 16 - -16 __pfx_bbr_cwnd_event 16 - -16 cubictcp_cwnd_event 80 - -80 bbr_cwnd_event 454 - -454 Total: Before=25240512, After=25240508, chg -0.00% Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260323234920.1097858-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- tools/testing/selftests/bpf/progs/bpf_cc_cubic.c | 8 +++--- tools/testing/selftests/bpf/progs/bpf_cubic.c | 33 +++++++++++------------- tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c | 16 +++++++++--- 3 files changed, 31 insertions(+), 26 deletions(-) (limited to 'tools/testing') diff --git a/tools/testing/selftests/bpf/progs/bpf_cc_cubic.c b/tools/testing/selftests/bpf/progs/bpf_cc_cubic.c index 9af19dfe4e80..bccf677b94b6 100644 --- a/tools/testing/selftests/bpf/progs/bpf_cc_cubic.c +++ b/tools/testing/selftests/bpf/progs/bpf_cc_cubic.c @@ -23,7 +23,7 @@ #define TCP_REORDERING (12) extern void cubictcp_init(struct sock *sk) __ksym; -extern void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) __ksym; +extern void cubictcp_cwnd_event_tx_start(struct sock *sk) __ksym; extern __u32 cubictcp_recalc_ssthresh(struct sock *sk) __ksym; extern void cubictcp_state(struct sock *sk, __u8 new_state) __ksym; extern __u32 tcp_reno_undo_cwnd(struct sock *sk) __ksym; @@ -108,9 +108,9 @@ void BPF_PROG(bpf_cubic_init, struct sock *sk) } SEC("struct_ops") -void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event) +void BPF_PROG(bpf_cubic_cwnd_event_tx_start, struct sock *sk) { - cubictcp_cwnd_event(sk, event); + cubictcp_cwnd_event_tx_start(sk); } SEC("struct_ops") @@ -172,7 +172,7 @@ struct tcp_congestion_ops cc_cubic = { .cong_control = (void *)bpf_cubic_cong_control, .set_state = (void *)bpf_cubic_state, .undo_cwnd = (void *)bpf_cubic_undo_cwnd, - .cwnd_event = (void *)bpf_cubic_cwnd_event, + .cwnd_event_tx_start = (void *)bpf_cubic_cwnd_event_tx_start, .pkts_acked = (void *)bpf_cubic_acked, .name = "bpf_cc_cubic", }; diff --git a/tools/testing/selftests/bpf/progs/bpf_cubic.c b/tools/testing/selftests/bpf/progs/bpf_cubic.c index 46fb2b37d3a7..ce18a4db813f 100644 --- a/tools/testing/selftests/bpf/progs/bpf_cubic.c +++ b/tools/testing/selftests/bpf/progs/bpf_cubic.c @@ -185,24 +185,21 @@ void BPF_PROG(bpf_cubic_init, struct sock *sk) } SEC("struct_ops") -void BPF_PROG(bpf_cubic_cwnd_event, struct sock *sk, enum tcp_ca_event event) +void BPF_PROG(bpf_cubic_cwnd_event_tx_start, struct sock *sk) { - if (event == CA_EVENT_TX_START) { - struct bpf_bictcp *ca = inet_csk_ca(sk); - __u32 now = tcp_jiffies32; - __s32 delta; - - delta = now - tcp_sk(sk)->lsndtime; - - /* We were application limited (idle) for a while. - * Shift epoch_start to keep cwnd growth to cubic curve. - */ - if (ca->epoch_start && delta > 0) { - ca->epoch_start += delta; - if (after(ca->epoch_start, now)) - ca->epoch_start = now; - } - return; + struct bpf_bictcp *ca = inet_csk_ca(sk); + __u32 now = tcp_jiffies32; + __s32 delta; + + delta = now - tcp_sk(sk)->lsndtime; + + /* We were application limited (idle) for a while. + * Shift epoch_start to keep cwnd growth to cubic curve. + */ + if (ca->epoch_start && delta > 0) { + ca->epoch_start += delta; + if (after(ca->epoch_start, now)) + ca->epoch_start = now; } } @@ -537,7 +534,7 @@ struct tcp_congestion_ops cubic = { .cong_avoid = (void *)bpf_cubic_cong_avoid, .set_state = (void *)bpf_cubic_state, .undo_cwnd = (void *)bpf_cubic_undo_cwnd, - .cwnd_event = (void *)bpf_cubic_cwnd_event, + .cwnd_event_tx_start = (void *)bpf_cubic_cwnd_event_tx_start, .pkts_acked = (void *)bpf_cubic_acked, .name = "bpf_cubic", }; diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c b/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c index f95862f570b7..0a3e9d35bf6f 100644 --- a/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c +++ b/tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c @@ -8,7 +8,7 @@ extern void bbr_init(struct sock *sk) __ksym; extern void bbr_main(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs) __ksym; extern u32 bbr_sndbuf_expand(struct sock *sk) __ksym; extern u32 bbr_undo_cwnd(struct sock *sk) __ksym; -extern void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) __ksym; +extern void bbr_cwnd_event_tx_start(struct sock *sk) __ksym; extern u32 bbr_ssthresh(struct sock *sk) __ksym; extern u32 bbr_min_tso_segs(struct sock *sk) __ksym; extern void bbr_set_state(struct sock *sk, u8 new_state) __ksym; @@ -16,6 +16,7 @@ extern void bbr_set_state(struct sock *sk, u8 new_state) __ksym; extern void dctcp_init(struct sock *sk) __ksym; extern void dctcp_update_alpha(struct sock *sk, u32 flags) __ksym; extern void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) __ksym; +extern void dctcp_cwnd_event_tx_start(struct sock *sk) __ksym; extern u32 dctcp_ssthresh(struct sock *sk) __ksym; extern u32 dctcp_cwnd_undo(struct sock *sk) __ksym; extern void dctcp_state(struct sock *sk, u8 new_state) __ksym; @@ -24,7 +25,7 @@ extern void cubictcp_init(struct sock *sk) __ksym; extern u32 cubictcp_recalc_ssthresh(struct sock *sk) __ksym; extern void cubictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) __ksym; extern void cubictcp_state(struct sock *sk, u8 new_state) __ksym; -extern void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) __ksym; +extern void cubictcp_cwnd_event_tx_start(struct sock *sk) __ksym; extern void cubictcp_acked(struct sock *sk, const struct ack_sample *sample) __ksym; SEC("struct_ops") @@ -69,9 +70,15 @@ u32 BPF_PROG(undo_cwnd, struct sock *sk) SEC("struct_ops") void BPF_PROG(cwnd_event, struct sock *sk, enum tcp_ca_event event) { - bbr_cwnd_event(sk, event); dctcp_cwnd_event(sk, event); - cubictcp_cwnd_event(sk, event); +} + +SEC("struct_ops") +void BPF_PROG(cwnd_event_tx_start, struct sock *sk) +{ + bbr_cwnd_event_tx_start(sk); + dctcp_cwnd_event_tx_start(sk); + cubictcp_cwnd_event_tx_start(sk); } SEC("struct_ops") @@ -111,6 +118,7 @@ struct tcp_congestion_ops tcp_ca_kfunc = { .sndbuf_expand = (void *)sndbuf_expand, .undo_cwnd = (void *)undo_cwnd, .cwnd_event = (void *)cwnd_event, + .cwnd_event_tx_start = (void *)cwnd_event_tx_start, .ssthresh = (void *)ssthresh, .min_tso_segs = (void *)min_tso_segs, .set_state = (void *)set_state, -- cgit v1.2.3