[PATCH mptcp-next 0/3] mptcp: misc improvement

[PATCH mptcp-next 0/3] mptcp: misc improvement

[Paolo Abeni]

This series is a follow-up the the discussion ongoing here:

https://github.com/multipath-tcp/mptcp_net-next/issues/437

Daire reported several sub-optimal MPTCP behaviour on high-latency
links.

At least 3 different items stands off:

* notsent_lowat setting fooling the scheduler
* sub-optimal send buffer autotuning
* delayed acks being de-facto disabled due to subflow rcvlowat

This series is an initial attempt to address the first 2 points above.
I have a tentative patch for the 3rd, but it's nowhere near passing
the self-tests, so it will have to wait a bit.

Sending out early after very little testing.

Paolo Abeni (3):
  mptcp: consolidate sockopt synchronization
  mptcp: ignore notsent_lowat setting at the subflow level.
  mptcp: refactor sndbuf auto-tuning.

 net/mptcp/protocol.c | 27 ++++++++++++++++++++++++---
 net/mptcp/protocol.h | 32 +++++++++++++++++++++++++++-----
 net/mptcp/sockopt.c  | 28 ++++++----------------------
 net/mptcp/subflow.c  | 21 ++++++++++-----------
 4 files changed, 67 insertions(+), 41 deletions(-)

-- 
2.41.0

[PATCH mptcp-next 1/3] mptcp: consolidate sockopt synchronization

[Paolo Abeni]

Move the socket option synchronization for active subflows
at subflow creation time. This allows removing the now unused
unlocked variant of such helper.

While at that, clean-up a bit the mptcp_subflow_create_socket()
errors path.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c |  2 --
 net/mptcp/sockopt.c  | 22 ----------------------
 net/mptcp/subflow.c  | 18 +++++++++---------
 3 files changed, 9 insertions(+), 33 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 3facdc006adc..3a905c122306 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -121,8 +121,6 @@ struct sock *__mptcp_nmpc_sk(struct mptcp_sock *msk)
 		ret = __mptcp_socket_create(msk);
 		if (ret)
 			return ERR_PTR(ret);
-
-		mptcp_sockopt_sync(msk, msk->first);
 	}
 
 	return msk->first;
diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 8260202c0066..f44b364b0055 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1444,28 +1444,6 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
 	inet_assign_bit(FREEBIND, ssk, inet_test_bit(FREEBIND, sk));
 }
 
-static void __mptcp_sockopt_sync(struct mptcp_sock *msk, struct sock *ssk)
-{
-	bool slow = lock_sock_fast(ssk);
-
-	sync_socket_options(msk, ssk);
-
-	unlock_sock_fast(ssk, slow);
-}
-
-void mptcp_sockopt_sync(struct mptcp_sock *msk, struct sock *ssk)
-{
-	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
-
-	msk_owned_by_me(msk);
-
-	if (READ_ONCE(subflow->setsockopt_seq) != msk->setsockopt_seq) {
-		__mptcp_sockopt_sync(msk, ssk);
-
-		subflow->setsockopt_seq = msk->setsockopt_seq;
-	}
-}
-
 void mptcp_sockopt_sync_locked(struct mptcp_sock *msk, struct sock *ssk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 918c1a235790..1c7ff7247bc0 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1525,8 +1525,6 @@ int __mptcp_subflow_connect(struct sock *sk, const struct mptcp_addr_info *loc,
 	if (addr.ss_family == AF_INET6)
 		addrlen = sizeof(struct sockaddr_in6);
 #endif
-	mptcp_sockopt_sync(msk, ssk);
-
 	ssk->sk_bound_dev_if = ifindex;
 	err = kernel_bind(sf, (struct sockaddr *)&addr, addrlen);
 	if (err)
@@ -1637,7 +1635,7 @@ int mptcp_subflow_create_socket(struct sock *sk, unsigned short family,
 
 	err = security_mptcp_add_subflow(sk, sf->sk);
 	if (err)
-		goto release_ssk;
+		goto err_free;
 
 	/* the newly created socket has to be in the same cgroup as its parent */
 	mptcp_attach_cgroup(sk, sf->sk);
@@ -1651,15 +1649,12 @@ int mptcp_subflow_create_socket(struct sock *sk, unsigned short family,
 	get_net_track(net, &sf->sk->ns_tracker, GFP_KERNEL);
 	sock_inuse_add(net, 1);
 	err = tcp_set_ulp(sf->sk, "mptcp");
+	if (err)
+		goto err_free;
 
-release_ssk:
+	mptcp_sockopt_sync_locked(mptcp_sk(sk), sf->sk);
 	release_sock(sf->sk);
 
-	if (err) {
-		sock_release(sf);
-		return err;
-	}
-
 	/* the newly created socket really belongs to the owning MPTCP master
 	 * socket, even if for additional subflows the allocation is performed
 	 * by a kernel workqueue. Adjust inode references, so that the
@@ -1679,6 +1674,11 @@ int mptcp_subflow_create_socket(struct sock *sk, unsigned short family,
 	mptcp_subflow_ops_override(sf->sk);
 
 	return 0;
+
+err_free:
+	release_sock(sf->sk);
+	sock_release(sf);
+	return err;
 }
 
 static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
-- 
2.41.0

[PATCH mptcp-next 2/3] mptcp: ignore notsent_lowat setting at the subflow level.

[Paolo Abeni]

Any latency related tuning taking action at the subflow level does
not really affect the user-space, as only the main MPTCP socket is
relevant.

Anyway any limiting setting may foul the MPTCP scheduler, not being
able to fully use the subflow-level cwin, leading to very poor b/w
usage.

Enforce notsent_lowat to be a no-op on every subflow.

Note that TCP_NOTSENT_LOWAT is currently not supported, and properly
dealing with that will require more invasive changes.

Singed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/sockopt.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index f44b364b0055..453d6c78c25c 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1450,6 +1450,12 @@ void mptcp_sockopt_sync_locked(struct mptcp_sock *msk, struct sock *ssk)
 
 	msk_owned_by_me(msk);
 
+	/* subflows must ignore any latency-related settings: will not affect
+	 * the user-space - only the msk is relevant - but will foul the
+	 * mptcp scheduler
+	 */
+	tcp_sk(ssk)->notsent_lowat = UINT_MAX;
+
 	if (READ_ONCE(subflow->setsockopt_seq) != msk->setsockopt_seq) {
 		sync_socket_options(msk, ssk);
 
-- 
2.41.0

[PATCH mptcp-next 3/3] mptcp: refactor sndbuf auto-tuning.

[Paolo Abeni]

The MPTCP protocol account for the data enqueued on all the subflows
to the main socket send buffer, while the send buffer auto-tuning
algorithm set the main socket send buffer size as the max size among
the subflows.

That causes bad performances when at least one subflow is sndbuf
limited, e.g. due to very high latency, as the MPTCP scheduler can't
even fill such buffer.

Change the send-buffer auto-tuning algorithm to compute the main socket
send buffer size as the sum of all the subflows buffer size.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 25 ++++++++++++++++++++++++-
 net/mptcp/protocol.h | 32 +++++++++++++++++++++++++++-----
 net/mptcp/subflow.c  |  3 +--
 3 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 3a905c122306..9683f11caa33 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -891,6 +891,7 @@ static bool __mptcp_finish_join(struct mptcp_sock *msk, struct sock *ssk)
 	mptcp_sockopt_sync_locked(msk, ssk);
 	mptcp_subflow_joined(msk, ssk);
 	mptcp_stop_tout_timer(sk);
+	__mptcp_propagate_sndbuf(sk, ssk);
 	return true;
 }
 
@@ -2403,6 +2404,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 		 * disconnect should never fail
 		 */
 		WARN_ON_ONCE(tcp_disconnect(ssk, 0));
+		__mptcp_propagate_sndbuf(sk, ssk);
 		mptcp_subflow_ctx_reset(subflow);
 		release_sock(ssk);
 
@@ -2427,6 +2429,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 	}
 
 out_release:
+	__mptcp_update_sndbuf(sk, -subflow->cached_sndbuf);
 	__mptcp_subflow_error_report(sk, ssk);
 	release_sock(ssk);
 
@@ -3214,7 +3217,7 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk,
 	 * uses the correct data
 	 */
 	mptcp_copy_inaddrs(nsk, ssk);
-	mptcp_propagate_sndbuf(nsk, ssk);
+	__mptcp_propagate_sndbuf(nsk, ssk);
 
 	mptcp_rcv_space_init(msk, ssk);
 	bh_unlock_sock(nsk);
@@ -3339,6 +3342,14 @@ void __mptcp_check_push(struct sock *sk, struct sock *ssk)
 		__set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->cb_flags);
 }
 
+void __mptcp_tune_sndbuf(struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
+	__mptcp_update_sndbuf(sk, msk->delta_sndbuf);
+	msk->delta_sndbuf = 0;
+}
+
 #define MPTCP_FLAGS_PROCESS_CTX_NEED (BIT(MPTCP_PUSH_PENDING) | \
 				      BIT(MPTCP_RETRANSMIT) | \
 				      BIT(MPTCP_FLUSH_JOIN_LIST))
@@ -3392,6 +3403,8 @@ static void mptcp_release_cb(struct sock *sk)
 			__mptcp_set_connected(sk);
 		if (__test_and_clear_bit(MPTCP_ERROR_REPORT, &msk->cb_flags))
 			__mptcp_error_report(sk);
+		if (__test_and_clear_bit(MPTCP_TUNE_SNDBUF, &msk->cb_flags))
+			__mptcp_tune_sndbuf(sk);
 	}
 
 	__mptcp_update_rmem(sk);
@@ -3437,6 +3450,15 @@ void mptcp_subflow_process_delegated(struct sock *ssk)
 		mptcp_data_unlock(sk);
 		mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_SEND);
 	}
+	if (test_bit(MPTCP_DELEGATE_SNDBUF, &subflow->delegated_status)) {
+		mptcp_data_lock(sk);
+		if (!sock_owned_by_user(sk))
+			__mptcp_propagate_sndbuf(sk, ssk);
+		else
+			__set_bit(MPTCP_TUNE_SNDBUF, &mptcp_sk(sk)->cb_flags);
+		mptcp_data_unlock(sk);
+		mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_SNDBUF);
+	}
 	if (test_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status)) {
 		schedule_3rdack_retransmission(ssk);
 		mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_ACK);
@@ -3523,6 +3545,7 @@ bool mptcp_finish_join(struct sock *ssk)
 	/* active subflow, already present inside the conn_list */
 	if (!list_empty(&subflow->node)) {
 		mptcp_subflow_joined(msk, ssk);
+		mptcp_propagate_sndbuf(parent, ssk);
 		return true;
 	}
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index aebc0cc24dad..02fb8b22c4ee 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -123,6 +123,7 @@
 #define MPTCP_RETRANSMIT	4
 #define MPTCP_FLUSH_JOIN_LIST	5
 #define MPTCP_CONNECTED		6
+#define MPTCP_TUNE_SNDBUF	7
 
 struct mptcp_skb_cb {
 	u64 map_seq;
@@ -320,6 +321,7 @@ struct mptcp_sock {
 		u64	rtt_us; /* last maximum rtt of subflows */
 	} rcvq_space;
 	u8		scaling_ratio;
+	int		delta_sndbuf;
 
 	u32		subflow_id;
 	u32		setsockopt_seq;
@@ -446,6 +448,7 @@ DECLARE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
 
 #define MPTCP_DELEGATE_SEND		0
 #define MPTCP_DELEGATE_ACK		1
+#define MPTCP_DELEGATE_SNDBUF		2
 
 /* MPTCP subflow context */
 struct mptcp_subflow_context {
@@ -518,6 +521,7 @@ struct mptcp_subflow_context {
 
 	u32	setsockopt_seq;
 	u32	stale_rcv_tstamp;
+	int     cached_sndbuf;
 
 	struct	sock *tcp_sock;	    /* tcp sk backpointer */
 	struct	sock *conn;	    /* parent mptcp_sock */
@@ -780,13 +784,31 @@ static inline bool mptcp_data_fin_enabled(const struct mptcp_sock *msk)
 	       READ_ONCE(msk->write_seq) == READ_ONCE(msk->snd_nxt);
 }
 
-static inline bool mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
+static inline void __mptcp_update_sndbuf(struct sock *sk, int delta)
 {
-	if ((sk->sk_userlocks & SOCK_SNDBUF_LOCK) || ssk->sk_sndbuf <= READ_ONCE(sk->sk_sndbuf))
-		return false;
+	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK) && delta)
+		WRITE_ONCE(sk->sk_sndbuf, sk->sk_sndbuf + delta);
+}
+
+static inline void __mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	int ssk_sndbuf = READ_ONCE(ssk->sk_sndbuf);
+
+	__mptcp_update_sndbuf(sk, ssk_sndbuf - subflow->cached_sndbuf);
+	subflow->cached_sndbuf = ssk_sndbuf;
+}
+
+static inline void mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+
+	if (likely(READ_ONCE(ssk->sk_sndbuf) == subflow->cached_sndbuf))
+		return;
 
-	WRITE_ONCE(sk->sk_sndbuf, ssk->sk_sndbuf);
-	return true;
+	local_bh_disable();
+	mptcp_subflow_delegate(subflow, MPTCP_DELEGATE_SNDBUF);
+	local_bh_enable();
 }
 
 static inline void mptcp_write_space(struct sock *sk)
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 1c7ff7247bc0..5a901f14e1d7 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -421,6 +421,7 @@ static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct soc
 
 void __mptcp_set_connected(struct sock *sk)
 {
+	__mptcp_propagate_sndbuf(sk, mptcp_sk(sk)->first);
 	if (sk->sk_state == TCP_SYN_SENT) {
 		inet_sk_state_store(sk, TCP_ESTABLISHED);
 		sk->sk_state_change(sk);
@@ -472,7 +473,6 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 		return;
 
 	msk = mptcp_sk(parent);
-	mptcp_propagate_sndbuf(parent, sk);
 	subflow->rel_write_seq = 1;
 	subflow->conn_finished = 1;
 	subflow->ssn_offset = TCP_SKB_CB(skb)->seq;
@@ -1728,7 +1728,6 @@ static void subflow_state_change(struct sock *sk)
 
 	msk = mptcp_sk(parent);
 	if (subflow_simultaneous_connect(sk)) {
-		mptcp_propagate_sndbuf(parent, sk);
 		mptcp_do_fallback(sk);
 		mptcp_rcv_space_init(msk, sk);
 		pr_fallback(msk);
-- 
2.41.0

Re: mptcp: refactor sndbuf auto-tuning.: Build Failure

[MPTCP CI]

Hi Paolo,

Thank you for your modifications, that's great!

But sadly, our CI spotted some issues with it when trying to build it.

You can find more details there:

  https://patchwork.kernel.org/project/mptcp/patch/a05184fa538535641415747b2d6bb83b5a772021.1694638162.git.pabeni@redhat.com/
  https://github.com/multipath-tcp/mptcp_net-next/actions/runs/6177982021

Status: failure
Initiator: MPTCPimporter
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/fbf3ee142d55

Feel free to reply to this email if you cannot access logs, if you need
some support to fix the error, if this doesn't seem to be caused by your
modifications or if the error is a false positive one.

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (Tessares)

Re: mptcp: refactor sndbuf auto-tuning.: Tests Results

[MPTCP CI]

Hi Paolo,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal (except selftest_mptcp_join):
  - Success! ✅:
  - Task: https://cirrus-ci.com/task/4811340401868800
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/4811340401868800/summary/summary.txt

- KVM Validation: debug (except selftest_mptcp_join):
  - Unstable: 3 failed test(s): packetdrill_fastopen packetdrill_regressions packetdrill_syscalls 🔴:
  - Task: https://cirrus-ci.com/task/5374290355290112
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/5374290355290112/summary/summary.txt

- KVM Validation: normal (only selftest_mptcp_join):
  - Success! ✅:
  - Task: https://cirrus-ci.com/task/5937240308711424
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/5937240308711424/summary/summary.txt

- KVM Validation: debug (only selftest_mptcp_join):
  - Success! ✅:
  - Task: https://cirrus-ci.com/task/6500190262132736
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/6500190262132736/summary/summary.txt

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/fbf3ee142d55


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-debug

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (Tessares)