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linux/include/trace/events/mptcp.h
Paolo Abeni d2000361e4 mptcp: better mptcp-level RTT estimator 
The current MPTCP-level RTT estimator has several issues. On high speed
links, the MPTCP-level receive buffer auto-tuning happens with a
frequency well above the TCP-level's one. That in turn can cause
excessive/unneeded receive buffer increase.

On such links, the initial rtt_us value is considerably higher than the
actual delay, and the current mptcp_rcv_space_adjust() updates
msk->rcvq_space.rtt_us with a period equal to the such field previous
value. If the initial rtt_us is 40ms, its first update will happen after
40ms, even if the subflows see actual RTT orders of magnitude lower.

Additionally:
- setting the msk RTT to the maximum among all the subflows RTTs makes
  DRS constantly overshooting the rcvbuf size when a subflow has
  considerable higher latency than the other(s).

- during unidirectional bulk transfers with multiple active subflows,
  the TCP-level RTT estimator occasionally sees considerably higher
  value than the real link delay, i.e. when the packet scheduler reacts
  to an incoming ACK on given subflow pushing data on a different
  subflow.

- currently inactive but still open subflows (i.e. switched to backup
  mode) are always considered when computing the msk-level RTT.

Address the all the issues above with a more accurate RTT estimation
strategy: the MPTCP-level RTT is set to the minimum of all the subflows
actually feeding data into the MPTCP receive buffer, using a small
sliding window.

While at it, also use EWMA to compute the msk-level scaling_ratio, to
that MPTCP can avoid traversing the subflow list is
mptcp_rcv_space_adjust().

Use some care to avoid updating msk and ssk level fields too often.

Fixes: a6b118febb ("mptcp: add receive buffer auto-tuning")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260407-net-next-mptcp-reduce-rbuf-v2-1-0d1d135bf6f6@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-04-08 19:32:00 -07:00

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/* SPDX-License-Identifier: GPL-2.0 */
#undef TRACE_SYSTEM
#define TRACE_SYSTEM mptcp
#if !defined(_TRACE_MPTCP_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_MPTCP_H
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <linux/tracepoint.h>
#include <net/ipv6.h>
#include <net/tcp.h>
#include <linux/sock_diag.h>
#include <net/rstreason.h>
#define show_mapping_status(status) \
__print_symbolic(status, \
{ 0, "MAPPING_OK" }, \
{ 1, "MAPPING_INVALID" }, \
{ 2, "MAPPING_EMPTY" }, \
{ 3, "MAPPING_DATA_FIN" }, \
{ 4, "MAPPING_DUMMY" })
TRACE_EVENT(mptcp_subflow_get_send,
TP_PROTO(struct mptcp_subflow_context *subflow),
TP_ARGS(subflow),
TP_STRUCT__entry(
__field(bool, active)
__field(bool, free)
__field(u32, snd_wnd)
__field(u32, pace)
__field(u8, backup)
__field(u64, ratio)
),
TP_fast_assign(
struct sock *ssk;
__entry->active = mptcp_subflow_active(subflow);
__entry->backup = subflow->backup || subflow->request_bkup;
if (subflow->tcp_sock && sk_fullsock(subflow->tcp_sock))
__entry->free = sk_stream_memory_free(subflow->tcp_sock);
else
__entry->free = 0;
ssk = mptcp_subflow_tcp_sock(subflow);
if (ssk && sk_fullsock(ssk)) {
__entry->snd_wnd = tcp_sk(ssk)->snd_wnd;
__entry->pace = READ_ONCE(ssk->sk_pacing_rate);
} else {
__entry->snd_wnd = 0;
__entry->pace = 0;
}
if (ssk && sk_fullsock(ssk) && __entry->pace)
__entry->ratio = div_u64((u64)ssk->sk_wmem_queued << 32, __entry->pace);
else
__entry->ratio = 0;
),
TP_printk("active=%d free=%d snd_wnd=%u pace=%u backup=%u ratio=%llu",
__entry->active, __entry->free,
__entry->snd_wnd, __entry->pace,
__entry->backup, __entry->ratio)
);
DECLARE_EVENT_CLASS(mptcp_dump_mpext,
TP_PROTO(struct mptcp_ext *mpext),
TP_ARGS(mpext),
TP_STRUCT__entry(
__field(u64, data_ack)
__field(u64, data_seq)
__field(u32, subflow_seq)
__field(u16, data_len)
__field(u16, csum)
__field(u8, use_map)
__field(u8, dsn64)
__field(u8, data_fin)
__field(u8, use_ack)
__field(u8, ack64)
__field(u8, mpc_map)
__field(u8, frozen)
__field(u8, reset_transient)
__field(u8, reset_reason)
__field(u8, csum_reqd)
__field(u8, infinite_map)
),
TP_fast_assign(
__entry->data_ack = mpext->ack64 ? mpext->data_ack : mpext->data_ack32;
__entry->data_seq = mpext->data_seq;
__entry->subflow_seq = mpext->subflow_seq;
__entry->data_len = mpext->data_len;
__entry->csum = (__force u16)mpext->csum;
__entry->use_map = mpext->use_map;
__entry->dsn64 = mpext->dsn64;
__entry->data_fin = mpext->data_fin;
__entry->use_ack = mpext->use_ack;
__entry->ack64 = mpext->ack64;
__entry->mpc_map = mpext->mpc_map;
__entry->frozen = mpext->frozen;
__entry->reset_transient = mpext->reset_transient;
__entry->reset_reason = mpext->reset_reason;
__entry->csum_reqd = mpext->csum_reqd;
__entry->infinite_map = mpext->infinite_map;
),
TP_printk("data_ack=%llu data_seq=%llu subflow_seq=%u data_len=%u csum=%x use_map=%u dsn64=%u data_fin=%u use_ack=%u ack64=%u mpc_map=%u frozen=%u reset_transient=%u reset_reason=%u csum_reqd=%u infinite_map=%u",
__entry->data_ack, __entry->data_seq,
__entry->subflow_seq, __entry->data_len,
__entry->csum, __entry->use_map,
__entry->dsn64, __entry->data_fin,
__entry->use_ack, __entry->ack64,
__entry->mpc_map, __entry->frozen,
__entry->reset_transient, __entry->reset_reason,
__entry->csum_reqd, __entry->infinite_map)
);
DEFINE_EVENT(mptcp_dump_mpext, mptcp_sendmsg_frag,
TP_PROTO(struct mptcp_ext *mpext),
TP_ARGS(mpext));
DEFINE_EVENT(mptcp_dump_mpext, get_mapping_status,
TP_PROTO(struct mptcp_ext *mpext),
TP_ARGS(mpext));
TRACE_EVENT(ack_update_msk,
TP_PROTO(u64 data_ack, u64 old_snd_una,
u64 new_snd_una, u64 new_wnd_end,
u64 msk_wnd_end),
TP_ARGS(data_ack, old_snd_una,
new_snd_una, new_wnd_end,
msk_wnd_end),
TP_STRUCT__entry(
__field(u64, data_ack)
__field(u64, old_snd_una)
__field(u64, new_snd_una)
__field(u64, new_wnd_end)
__field(u64, msk_wnd_end)
),
TP_fast_assign(
__entry->data_ack = data_ack;
__entry->old_snd_una = old_snd_una;
__entry->new_snd_una = new_snd_una;
__entry->new_wnd_end = new_wnd_end;
__entry->msk_wnd_end = msk_wnd_end;
),
TP_printk("data_ack=%llu old_snd_una=%llu new_snd_una=%llu new_wnd_end=%llu msk_wnd_end=%llu",
__entry->data_ack, __entry->old_snd_una,
__entry->new_snd_una, __entry->new_wnd_end,
__entry->msk_wnd_end)
);
TRACE_EVENT(subflow_check_data_avail,
TP_PROTO(__u8 status, struct sk_buff *skb),
TP_ARGS(status, skb),
TP_STRUCT__entry(
__field(u8, status)
__field(const void *, skb)
),
TP_fast_assign(
__entry->status = status;
__entry->skb = skb;
),
TP_printk("mapping_status=%s, skb=%p",
show_mapping_status(__entry->status),
__entry->skb)
);
#include <trace/events/net_probe_common.h>
TRACE_EVENT(mptcp_rcvbuf_grow,
TP_PROTO(struct sock *sk, int time),
TP_ARGS(sk, time),
TP_STRUCT__entry(
__field(int, time)
__field(__u32, rtt_us)
__field(__u32, copied)
__field(__u32, inq)
__field(__u32, space)
__field(__u32, ooo_space)
__field(__u32, rcvbuf)
__field(__u32, rcv_wnd)
__field(__u8, scaling_ratio)
__field(__u16, sport)
__field(__u16, dport)
__field(__u16, family)
__array(__u8, saddr, 4)
__array(__u8, daddr, 4)
__array(__u8, saddr_v6, 16)
__array(__u8, daddr_v6, 16)
__field(const void *, skaddr)
),
TP_fast_assign(
struct mptcp_sock *msk = mptcp_sk(sk);
struct inet_sock *inet = inet_sk(sk);
bool ofo_empty;
__be32 *p32;
__entry->time = time;
__entry->rtt_us = mptcp_rtt_us_est(msk) >> 3;
__entry->copied = msk->rcvq_space.copied;
__entry->inq = mptcp_inq_hint(sk);
__entry->space = msk->rcvq_space.space;
ofo_empty = RB_EMPTY_ROOT(&msk->out_of_order_queue);
__entry->ooo_space = ofo_empty ? 0 :
MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq -
msk->ack_seq;
__entry->rcvbuf = sk->sk_rcvbuf;
__entry->rcv_wnd = atomic64_read(&msk->rcv_wnd_sent) -
msk->ack_seq;
__entry->scaling_ratio = msk->scaling_ratio;
__entry->sport = ntohs(inet->inet_sport);
__entry->dport = ntohs(inet->inet_dport);
__entry->family = sk->sk_family;
p32 = (__be32 *)__entry->saddr;
*p32 = inet->inet_saddr;
p32 = (__be32 *)__entry->daddr;
*p32 = inet->inet_daddr;
TP_STORE_ADDRS(__entry, inet->inet_saddr, inet->inet_daddr,
sk->sk_v6_rcv_saddr, sk->sk_v6_daddr);
__entry->skaddr = sk;
),
TP_printk("time=%u rtt_us=%u copied=%u inq=%u space=%u ooo=%u scaling_ratio=%u "
"rcvbuf=%u rcv_wnd=%u family=%d sport=%hu dport=%hu saddr=%pI4 "
"daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c skaddr=%p",
__entry->time, __entry->rtt_us, __entry->copied,
__entry->inq, __entry->space, __entry->ooo_space,
__entry->scaling_ratio, __entry->rcvbuf, __entry->rcv_wnd,
__entry->family, __entry->sport, __entry->dport,
__entry->saddr, __entry->daddr, __entry->saddr_v6,
__entry->daddr_v6, __entry->skaddr)
);
#endif /* _TRACE_MPTCP_H */
/* This part must be outside protection */
#include <trace/define_trace.h>
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