From: Eric Dumazet Date: Mon, 23 Mar 2026 23:49:20 +0000 (+0000) Subject: tcp: add cwnd_event_tx_start to tcp_congestion_ops X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d1e59a46973719e458bec78d00dd767d7a7ba71f;p=thirdparty%2Flinux.git 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 --- diff --git a/include/net/tcp.h b/include/net/tcp.h index f87bdacb5a699..39ff4cf3c810f 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1341,6 +1341,9 @@ struct tcp_congestion_ops { /* call when cwnd event occurs (optional) */ void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev); + /* call when CA_EVENT_TX_START cwnd event occurs (optional) */ + void (*cwnd_event_tx_start)(struct sock *sk); + /* call when ack arrives (optional) */ void (*in_ack_event)(struct sock *sk, u32 flags); @@ -1440,6 +1443,11 @@ static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event) { const struct inet_connection_sock *icsk = inet_csk(sk); + if (event == CA_EVENT_TX_START) { + if (icsk->icsk_ca_ops->cwnd_event_tx_start) + icsk->icsk_ca_ops->cwnd_event_tx_start(sk); + return; + } if (icsk->icsk_ca_ops->cwnd_event) icsk->icsk_ca_ops->cwnd_event(sk, event); } diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c index e01492234b0b3..008edc7f66885 100644 --- a/net/ipv4/bpf_tcp_ca.c +++ b/net/ipv4/bpf_tcp_ca.c @@ -272,6 +272,10 @@ static void bpf_tcp_ca_cwnd_event(struct sock *sk, enum tcp_ca_event ev) { } +static void bpf_tcp_ca_cwnd_event_tx_start(struct sock *sk) +{ +} + static void bpf_tcp_ca_in_ack_event(struct sock *sk, u32 flags) { } @@ -313,6 +317,7 @@ static struct tcp_congestion_ops __bpf_ops_tcp_congestion_ops = { .cong_avoid = bpf_tcp_ca_cong_avoid, .set_state = bpf_tcp_ca_set_state, .cwnd_event = bpf_tcp_ca_cwnd_event, + .cwnd_event_tx_start = bpf_tcp_ca_cwnd_event_tx_start, .in_ack_event = bpf_tcp_ca_in_ack_event, .pkts_acked = bpf_tcp_ca_pkts_acked, .min_tso_segs = bpf_tcp_ca_min_tso_segs, diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 05d52372ca8fb..1ddc20a399b07 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -330,12 +330,12 @@ static void bbr_save_cwnd(struct sock *sk) bbr->prior_cwnd = max(bbr->prior_cwnd, tcp_snd_cwnd(tp)); } -__bpf_kfunc static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) +__bpf_kfunc static void bbr_cwnd_event_tx_start(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct bbr *bbr = inet_csk_ca(sk); - if (event == CA_EVENT_TX_START && tp->app_limited) { + if (tp->app_limited) { bbr->idle_restart = 1; bbr->ack_epoch_mstamp = tp->tcp_mstamp; bbr->ack_epoch_acked = 0; @@ -1149,7 +1149,7 @@ static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = { .cong_control = bbr_main, .sndbuf_expand = bbr_sndbuf_expand, .undo_cwnd = bbr_undo_cwnd, - .cwnd_event = bbr_cwnd_event, + .cwnd_event_tx_start = bbr_cwnd_event_tx_start, .ssthresh = bbr_ssthresh, .min_tso_segs = bbr_min_tso_segs, .get_info = bbr_get_info, @@ -1161,7 +1161,7 @@ BTF_ID_FLAGS(func, bbr_init) BTF_ID_FLAGS(func, bbr_main) BTF_ID_FLAGS(func, bbr_sndbuf_expand) BTF_ID_FLAGS(func, bbr_undo_cwnd) -BTF_ID_FLAGS(func, bbr_cwnd_event) +BTF_ID_FLAGS(func, bbr_cwnd_event_tx_start) BTF_ID_FLAGS(func, bbr_ssthresh) BTF_ID_FLAGS(func, bbr_min_tso_segs) BTF_ID_FLAGS(func, bbr_set_state) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index 76c23675ae50a..ab78b5ae8d0e3 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -139,24 +139,21 @@ __bpf_kfunc static void cubictcp_init(struct sock *sk) tcp_sk(sk)->snd_ssthresh = initial_ssthresh; } -__bpf_kfunc static void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) +__bpf_kfunc static void cubictcp_cwnd_event_tx_start(struct sock *sk) { - if (event == CA_EVENT_TX_START) { - struct 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 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; } } @@ -481,7 +478,7 @@ static struct tcp_congestion_ops cubictcp __read_mostly = { .cong_avoid = cubictcp_cong_avoid, .set_state = cubictcp_state, .undo_cwnd = tcp_reno_undo_cwnd, - .cwnd_event = cubictcp_cwnd_event, + .cwnd_event_tx_start = cubictcp_cwnd_event_tx_start, .pkts_acked = cubictcp_acked, .owner = THIS_MODULE, .name = "cubic", @@ -492,7 +489,7 @@ BTF_ID_FLAGS(func, cubictcp_init) BTF_ID_FLAGS(func, cubictcp_recalc_ssthresh) BTF_ID_FLAGS(func, cubictcp_cong_avoid) BTF_ID_FLAGS(func, cubictcp_state) -BTF_ID_FLAGS(func, cubictcp_cwnd_event) +BTF_ID_FLAGS(func, cubictcp_cwnd_event_tx_start) BTF_ID_FLAGS(func, cubictcp_acked) BTF_KFUNCS_END(tcp_cubic_check_kfunc_ids) diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c index 03abe0848420d..96c99999e09dd 100644 --- a/net/ipv4/tcp_dctcp.c +++ b/net/ipv4/tcp_dctcp.c @@ -203,15 +203,19 @@ __bpf_kfunc static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev) tcp_plb_update_state_upon_rto(sk, &ca->plb); dctcp_react_to_loss(sk); break; - case CA_EVENT_TX_START: - tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */ - break; default: /* Don't care for the rest. */ break; } } +__bpf_kfunc static void dctcp_cwnd_event_tx_start(struct sock *sk) +{ + struct dctcp *ca = inet_csk_ca(sk); + + tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */ +} + static size_t dctcp_get_info(struct sock *sk, u32 ext, int *attr, union tcp_cc_info *info) { @@ -252,6 +256,7 @@ static struct tcp_congestion_ops dctcp __read_mostly = { .init = dctcp_init, .in_ack_event = dctcp_update_alpha, .cwnd_event = dctcp_cwnd_event, + .cwnd_event_tx_start = dctcp_cwnd_event_tx_start, .ssthresh = dctcp_ssthresh, .cong_avoid = tcp_reno_cong_avoid, .undo_cwnd = dctcp_cwnd_undo, @@ -275,6 +280,7 @@ BTF_KFUNCS_START(tcp_dctcp_check_kfunc_ids) BTF_ID_FLAGS(func, dctcp_init) BTF_ID_FLAGS(func, dctcp_update_alpha) BTF_ID_FLAGS(func, dctcp_cwnd_event) +BTF_ID_FLAGS(func, dctcp_cwnd_event_tx_start) BTF_ID_FLAGS(func, dctcp_ssthresh) BTF_ID_FLAGS(func, dctcp_cwnd_undo) BTF_ID_FLAGS(func, dctcp_state) diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c index 786848ad37ea8..cf12fb6be079d 100644 --- a/net/ipv4/tcp_vegas.c +++ b/net/ipv4/tcp_vegas.c @@ -151,12 +151,17 @@ EXPORT_SYMBOL_GPL(tcp_vegas_state); */ void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event) { - if (event == CA_EVENT_CWND_RESTART || - event == CA_EVENT_TX_START) + if (event == CA_EVENT_CWND_RESTART) tcp_vegas_init(sk); } EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event); +void tcp_vegas_cwnd_event_tx_start(struct sock *sk) +{ + tcp_vegas_init(sk); +} +EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event_tx_start); + static inline u32 tcp_vegas_ssthresh(struct tcp_sock *tp) { return min(tp->snd_ssthresh, tcp_snd_cwnd(tp)); diff --git a/net/ipv4/tcp_vegas.h b/net/ipv4/tcp_vegas.h index 4f24d0e37d9c1..602af8e600c7f 100644 --- a/net/ipv4/tcp_vegas.h +++ b/net/ipv4/tcp_vegas.h @@ -20,6 +20,7 @@ void tcp_vegas_init(struct sock *sk); void tcp_vegas_state(struct sock *sk, u8 ca_state); void tcp_vegas_pkts_acked(struct sock *sk, const struct ack_sample *sample); void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event); +void tcp_vegas_cwnd_event_tx_start(struct sock *sk); size_t tcp_vegas_get_info(struct sock *sk, u32 ext, int *attr, union tcp_cc_info *info); diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c index 366ff6f214b2e..1b2e1b947901f 100644 --- a/net/ipv4/tcp_veno.c +++ b/net/ipv4/tcp_veno.c @@ -112,10 +112,15 @@ static void tcp_veno_state(struct sock *sk, u8 ca_state) */ static void tcp_veno_cwnd_event(struct sock *sk, enum tcp_ca_event event) { - if (event == CA_EVENT_CWND_RESTART || event == CA_EVENT_TX_START) + if (event == CA_EVENT_CWND_RESTART) tcp_veno_init(sk); } +static void tcp_veno_cwnd_event_tx_start(struct sock *sk) +{ + tcp_veno_init(sk); +} + static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked) { struct tcp_sock *tp = tcp_sk(sk); @@ -213,6 +218,7 @@ static struct tcp_congestion_ops tcp_veno __read_mostly = { .pkts_acked = tcp_veno_pkts_acked, .set_state = tcp_veno_state, .cwnd_event = tcp_veno_cwnd_event, + .cwnd_event_tx_start = tcp_veno_cwnd_event_tx_start, .owner = THIS_MODULE, .name = "veno", diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c index 18b07ff5d20e6..b22b3dccd05ef 100644 --- a/net/ipv4/tcp_yeah.c +++ b/net/ipv4/tcp_yeah.c @@ -212,6 +212,7 @@ static struct tcp_congestion_ops tcp_yeah __read_mostly = { .cong_avoid = tcp_yeah_cong_avoid, .set_state = tcp_vegas_state, .cwnd_event = tcp_vegas_cwnd_event, + .cwnd_event_tx_start = tcp_vegas_cwnd_event_tx_start, .get_info = tcp_vegas_get_info, .pkts_acked = tcp_vegas_pkts_acked, diff --git a/tools/testing/selftests/bpf/progs/bpf_cc_cubic.c b/tools/testing/selftests/bpf/progs/bpf_cc_cubic.c index 9af19dfe4e80b..bccf677b94b61 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 46fb2b37d3a70..ce18a4db813fa 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 f95862f570b73..0a3e9d35bf6f0 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,