* [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops
@ 2026-03-23 23:49 Eric Dumazet
2026-03-25 4:10 ` patchwork-bot+netdevbpf
2026-03-25 6:32 ` kernel test robot
0 siblings, 2 replies; 3+ messages in thread
From: Eric Dumazet @ 2026-03-23 23:49 UTC (permalink / raw)
To: David S . Miller, Jakub Kicinski, Paolo Abeni
Cc: Simon Horman, Neal Cardwell, Kuniyuki Iwashima, Martin KaFai Lau,
netdev, eric.dumazet, Eric Dumazet
(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 <edumazet@google.com>
---
v4: more eBPF fixes in net/ipv4/bpf_tcp_ca.c
v3: fix tools/testing/selftests/bpf/progs/tcp_ca_kfunc.c (Jakub)
v2: fix tools/testing/selftests/bpf/progs/bpf_cc_cubic.c (Jakub)
v1: https://lore.kernel.org/netdev/20260313202802.1201129-1-edumazet@google.com/
include/net/tcp.h | 8 +++++
net/ipv4/bpf_tcp_ca.c | 5 +++
net/ipv4/tcp_bbr.c | 8 ++---
net/ipv4/tcp_cubic.c | 35 +++++++++----------
net/ipv4/tcp_dctcp.c | 12 +++++--
net/ipv4/tcp_vegas.c | 9 +++--
net/ipv4/tcp_vegas.h | 1 +
net/ipv4/tcp_veno.c | 8 ++++-
net/ipv4/tcp_yeah.c | 1 +
.../selftests/bpf/progs/bpf_cc_cubic.c | 8 ++---
tools/testing/selftests/bpf/progs/bpf_cubic.c | 33 ++++++++---------
.../selftests/bpf/progs/tcp_ca_kfunc.c | 16 ++++++---
12 files changed, 89 insertions(+), 55 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index f87bdacb5a6995422851e88cfb65734702c84093..39ff4cf3c810f5619a479dcd92192043374a1739 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 e01492234b0b349498f8e56c2f07d8bba092c00e..008edc7f6688523dc86963d90485655e9fa8374e 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 05d52372ca8fb068530a9b3379f1ae0f9d0b362a..1ddc20a399b07054f8175b5f6459f8ae6dbf34bb 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 76c23675ae50ab50c977dc1de79a3df57db98ef6..ab78b5ae8d0e3d13a39bd1adf1e105b84f806b63 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 03abe0848420d7fb7b514e6ad24f4c702954ab14..96c99999e09dde9de9c337e4d6c692f517467c7b 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 786848ad37ea8d5f9bd817666181905f3f6ec9d4..cf12fb6be079d8ccd65f297a3a90a9a5e90036e8 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 4f24d0e37d9c1e9d5336e8e99253e660143362c9..602af8e600c7f85603ff1a53008e1144617ea14b 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 366ff6f214b2ee746cecdf10353e4624252478e0..1b2e1b947901f3ca6004aced8e6d39c131f1fb68 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 18b07ff5d20e6c5eefe9ab54c6b8e429f01d64b9..b22b3dccd05efddfe11203578950eddecee14887 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 9af19dfe4e80b00bc09fe40c7d6c9642cdfb4a23..bccf677b94b61226a3dd0517e0b2e64168de711f 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 46fb2b37d3a70671485af37ed700a991c0975cd2..ce18a4db813fab877aec0c73d72cc9c958312ad3 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 f95862f570b73f4c86fa6d7b6a912c4b055d02fb..0a3e9d35bf6f0c4c988c741c010fb7f3405fb43c 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,
--
2.53.0.983.g0bb29b3bc5-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops
2026-03-23 23:49 [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops Eric Dumazet
@ 2026-03-25 4:10 ` patchwork-bot+netdevbpf
2026-03-25 6:32 ` kernel test robot
1 sibling, 0 replies; 3+ messages in thread
From: patchwork-bot+netdevbpf @ 2026-03-25 4:10 UTC (permalink / raw)
To: Eric Dumazet
Cc: davem, kuba, pabeni, horms, ncardwell, kuniyu, martin.lau, netdev,
eric.dumazet
Hello:
This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:
On Mon, 23 Mar 2026 23:49:20 +0000 you wrote:
> (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.
>
> [...]
Here is the summary with links:
- [v4,net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops
https://git.kernel.org/netdev/net-next/c/d1e59a469737
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops
2026-03-23 23:49 [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops Eric Dumazet
2026-03-25 4:10 ` patchwork-bot+netdevbpf
@ 2026-03-25 6:32 ` kernel test robot
1 sibling, 0 replies; 3+ messages in thread
From: kernel test robot @ 2026-03-25 6:32 UTC (permalink / raw)
To: Eric Dumazet, David S . Miller, Jakub Kicinski, Paolo Abeni
Cc: oe-kbuild-all, Simon Horman, Neal Cardwell, Kuniyuki Iwashima,
Martin KaFai Lau, netdev, eric.dumazet, Eric Dumazet
Hi Eric,
kernel test robot noticed the following build warnings:
[auto build test WARNING on net-next/main]
url: https://github.com/intel-lab-lkp/linux/commits/Eric-Dumazet/tcp-add-cwnd_event_tx_start-to-tcp_congestion_ops/20260325-042334
base: net-next/main
patch link: https://lore.kernel.org/r/20260323234920.1097858-1-edumazet%40google.com
patch subject: [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops
config: i386-randconfig-141-20260325 (https://download.01.org/0day-ci/archive/20260325/202603251430.gQ3VuiKV-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
smatch: v0.5.0-9004-gb810ac53
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603251430.gQ3VuiKV-lkp@intel.com/
New smatch warnings:
include/net/tcp.h:1449 tcp_ca_event() warn: inconsistent indenting
include/net/tcp.h:1449 tcp_ca_event() warn: inconsistent indenting
Old smatch warnings:
net/ipv4/tcp_output.c:779 tcp_options_write() error: we previously assumed 'tp' could be null (see line 747)
vim +1449 include/net/tcp.h
1441
1442 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
1443 {
1444 const struct inet_connection_sock *icsk = inet_csk(sk);
1445
1446 if (event == CA_EVENT_TX_START) {
1447 if (icsk->icsk_ca_ops->cwnd_event_tx_start)
1448 icsk->icsk_ca_ops->cwnd_event_tx_start(sk);
> 1449 return;
1450 }
1451 if (icsk->icsk_ca_ops->cwnd_event)
1452 icsk->icsk_ca_ops->cwnd_event(sk, event);
1453 }
1454
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-03-23 23:49 [PATCH v4 net-next] tcp: add cwnd_event_tx_start to tcp_congestion_ops Eric Dumazet
2026-03-25 4:10 ` patchwork-bot+netdevbpf
2026-03-25 6:32 ` kernel test robot
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