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Message-Id: <20250927-net-next-mptcp-rcv-path-imp-v1-3-5da266aa9c1a@kernel.org>
Date: Sat, 27 Sep 2025 11:40:39 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang@...nel.org>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>, Neal Cardwell <ncardwell@...gle.com>,
Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>,
Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org, mptcp@...ts.linux.dev,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
"Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH net-next 3/8] mptcp: rcvbuf auto-tuning improvement
From: Paolo Abeni <pabeni@...hat.com>
Apply to the MPTCP auto-tuning the same improvements introduced for the
TCP protocol by the merge commit 2da35e4b4df9 ("Merge branch
'tcp-receive-side-improvements'").
The main difference is that TCP subflow and the main MPTCP socket need
to account separately for OoO: MPTCP does not care for TCP-level OoO
and vice versa, as a consequence do not reflect MPTCP-level rcvbuf
increase due to OoO packets at the subflow level.
This refeactor additionally allow dropping the msk receive buffer update
at receive time, as the latter only intended to cope with subflow receive
buffer increase due to OoO packets.
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/487
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/559
Reviewed-by: Geliang Tang <geliang@...nel.org>
Tested-by: Geliang Tang <geliang@...nel.org>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
net/mptcp/protocol.c | 97 +++++++++++++++++++++++++---------------------------
net/mptcp/protocol.h | 4 +--
2 files changed, 49 insertions(+), 52 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 62cdd2bcff9da12783b97fd40813ede85b5c83d9..f994e7f45f7b96c280708d7a29c1423a91e4cfee 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -179,6 +179,35 @@ static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
return mptcp_try_coalesce((struct sock *)msk, to, from);
}
+/* "inspired" by tcp_rcvbuf_grow(), main difference:
+ * - mptcp does not maintain a msk-level window clamp
+ * - returns true when the receive buffer is actually updated
+ */
+static bool mptcp_rcvbuf_grow(struct sock *sk)
+{
+ struct mptcp_sock *msk = mptcp_sk(sk);
+ const struct net *net = sock_net(sk);
+ int rcvwin, rcvbuf, cap;
+
+ if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||
+ (sk->sk_userlocks & SOCK_RCVBUF_LOCK))
+ return false;
+
+ rcvwin = msk->rcvq_space.space << 1;
+
+ if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
+ rcvwin += MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq - msk->ack_seq;
+
+ cap = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
+
+ rcvbuf = min_t(u32, mptcp_space_from_win(sk, rcvwin), cap);
+ if (rcvbuf > sk->sk_rcvbuf) {
+ WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
+ return true;
+ }
+ return false;
+}
+
/* "inspired" by tcp_data_queue_ofo(), main differences:
* - use mptcp seqs
* - don't cope with sacks
@@ -292,6 +321,9 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
end:
skb_condense(skb);
skb_set_owner_r(skb, sk);
+ /* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */
+ if (sk->sk_socket)
+ mptcp_rcvbuf_grow(sk);
}
static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
@@ -784,18 +816,10 @@ static bool move_skbs_to_msk(struct mptcp_sock *msk, struct sock *ssk)
return moved;
}
-static void __mptcp_rcvbuf_update(struct sock *sk, struct sock *ssk)
-{
- if (unlikely(ssk->sk_rcvbuf > sk->sk_rcvbuf))
- WRITE_ONCE(sk->sk_rcvbuf, ssk->sk_rcvbuf);
-}
-
static void __mptcp_data_ready(struct sock *sk, struct sock *ssk)
{
struct mptcp_sock *msk = mptcp_sk(sk);
- __mptcp_rcvbuf_update(sk, ssk);
-
/* Wake-up the reader only for in-sequence data */
if (move_skbs_to_msk(msk, ssk) && mptcp_epollin_ready(sk))
sk->sk_data_ready(sk);
@@ -2014,48 +2038,26 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
if (msk->rcvq_space.copied <= msk->rcvq_space.space)
goto new_measure;
- if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
- !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
- u64 rcvwin, grow;
- int rcvbuf;
+ msk->rcvq_space.space = msk->rcvq_space.copied;
+ if (mptcp_rcvbuf_grow(sk)) {
- rcvwin = ((u64)msk->rcvq_space.copied << 1) + 16 * advmss;
+ /* Make subflows follow along. If we do not do this, we
+ * get drops at subflow level if skbs can't be moved to
+ * the mptcp rx queue fast enough (announced rcv_win can
+ * exceed ssk->sk_rcvbuf).
+ */
+ mptcp_for_each_subflow(msk, subflow) {
+ struct sock *ssk;
+ bool slow;
- grow = rcvwin * (msk->rcvq_space.copied - msk->rcvq_space.space);
-
- do_div(grow, msk->rcvq_space.space);
- rcvwin += (grow << 1);
-
- rcvbuf = min_t(u64, mptcp_space_from_win(sk, rcvwin),
- READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
-
- if (rcvbuf > sk->sk_rcvbuf) {
- u32 window_clamp;
-
- window_clamp = mptcp_win_from_space(sk, rcvbuf);
- WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
-
- /* Make subflows follow along. If we do not do this, we
- * get drops at subflow level if skbs can't be moved to
- * the mptcp rx queue fast enough (announced rcv_win can
- * exceed ssk->sk_rcvbuf).
- */
- mptcp_for_each_subflow(msk, subflow) {
- struct sock *ssk;
- bool slow;
-
- ssk = mptcp_subflow_tcp_sock(subflow);
- slow = lock_sock_fast(ssk);
- WRITE_ONCE(ssk->sk_rcvbuf, rcvbuf);
- WRITE_ONCE(tcp_sk(ssk)->window_clamp, window_clamp);
- if (tcp_can_send_ack(ssk))
- tcp_cleanup_rbuf(ssk, 1);
- unlock_sock_fast(ssk, slow);
- }
+ ssk = mptcp_subflow_tcp_sock(subflow);
+ slow = lock_sock_fast(ssk);
+ tcp_sk(ssk)->rcvq_space.space = msk->rcvq_space.copied;
+ tcp_rcvbuf_grow(ssk);
+ unlock_sock_fast(ssk, slow);
}
}
- msk->rcvq_space.space = msk->rcvq_space.copied;
new_measure:
msk->rcvq_space.copied = 0;
msk->rcvq_space.time = mstamp;
@@ -2084,11 +2086,6 @@ static bool __mptcp_move_skbs(struct sock *sk)
if (list_empty(&msk->conn_list))
return false;
- /* verify we can move any data from the subflow, eventually updating */
- if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
- mptcp_for_each_subflow(msk, subflow)
- __mptcp_rcvbuf_update(sk, subflow->tcp_sock);
-
subflow = list_first_entry(&msk->conn_list,
struct mptcp_subflow_context, node);
for (;;) {
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 371084a3fc225391fe98ad42a2e2f63465119989..52f9cfa4ce95c789a7b9c53c47095abe7964d18f 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -341,8 +341,8 @@ struct mptcp_sock {
struct mptcp_pm_data pm;
struct mptcp_sched_ops *sched;
struct {
- u32 space; /* bytes copied in last measurement window */
- u32 copied; /* bytes copied in this measurement window */
+ int space; /* bytes copied in last measurement window */
+ int copied; /* bytes copied in this measurement window */
u64 time; /* start time of measurement window */
u64 rtt_us; /* last maximum rtt of subflows */
} rcvq_space;
--
2.51.0
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