[PATCH mptcp-next 0/4] refactor push pending

[PATCH mptcp-next 0/4] refactor push pending

[Geliang Tang]

Refactor __mptcp_push_pending() and __mptcp_subflow_push_pending() to
remove duplicate code and support redundant scheduler more easily in
__mptcp_subflow_push_pending().

Geliang Tang (4):
  mptcp: update __mptcp_push_pending
  mptcp: add do_push_pending helper
  mptcp: update __mptcp_subflow_push_pending
  mptcp: simplify __mptcp_subflow_push_pending

 net/mptcp/protocol.c | 137 ++++++++++++++++---------------------------
 1 file changed, 50 insertions(+), 87 deletions(-)

-- 
2.35.3

[PATCH mptcp-next 1/4] mptcp: update __mptcp_push_pending

[Geliang Tang]

To support redundant package schedulers more easily, this patch moves the
packet scheduler out of the dfrags loop in __mptcp_push_pending(), invoke
mptcp_sched_get_send() only once. And update the socket locks
correspondingly.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c | 33 +++++++++++----------------------
 1 file changed, 11 insertions(+), 22 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 7ca21915b3d1..fc972d56926e 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1530,15 +1530,24 @@ void mptcp_check_and_set_pending(struct sock *sk)
 
 void __mptcp_push_pending(struct sock *sk, unsigned int flags)
 {
-	struct sock *prev_ssk = NULL, *ssk = NULL;
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct mptcp_sendmsg_info info = {
 				.flags = flags,
 	};
 	bool do_check_data_fin = false;
 	struct mptcp_data_frag *dfrag;
+	struct sock *ssk;
 	int len;
 
+	ssk = mptcp_sched_get_send(msk);
+	if (!ssk)
+		goto out;
+
+	if (!mptcp_send_head(sk))
+		goto out;
+
+	lock_sock(ssk);
+
 	while ((dfrag = mptcp_send_head(sk))) {
 		info.sent = dfrag->already_sent;
 		info.limit = dfrag->data_len;
@@ -1546,24 +1555,6 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
 		while (len > 0) {
 			int ret = 0;
 
-			prev_ssk = ssk;
-			ssk = mptcp_sched_get_send(msk);
-
-			/* First check. If the ssk has changed since
-			 * the last round, release prev_ssk
-			 */
-			if (ssk != prev_ssk && prev_ssk)
-				mptcp_push_release(prev_ssk, &info);
-			if (!ssk)
-				goto out;
-
-			/* Need to lock the new subflow only if different
-			 * from the previous one, otherwise we are still
-			 * helding the relevant lock
-			 */
-			if (ssk != prev_ssk)
-				lock_sock(ssk);
-
 			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
 			if (ret <= 0) {
 				if (ret == -EAGAIN)
@@ -1581,9 +1572,7 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
 		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
 	}
 
-	/* at this point we held the socket lock for the last subflow we used */
-	if (ssk)
-		mptcp_push_release(ssk, &info);
+	mptcp_push_release(ssk, &info);
 
 out:
 	/* ensure the rtx timer is running */
-- 
2.35.3

Re: [PATCH mptcp-next 1/4] mptcp: update __mptcp_push_pending

[Paolo Abeni]

On Wed, 2022-09-28 at 17:48 +0800, Geliang Tang wrote:
> To support redundant package schedulers more easily, this patch moves the
> packet scheduler out of the dfrags loop in __mptcp_push_pending(), invoke
> mptcp_sched_get_send() only once. 

I fear the above will make cause hitting HoL blocking [more]
frequently/easily. I'm not sure if the simult_flows.sh self test will
catch that, but you should see a measurably worse running time for such
test - in non debug build, as the average of multiple runs.

I'm sorry, I can't see a feasible way out here :(

/P

Re: [PATCH mptcp-next 1/4] mptcp: update __mptcp_push_pending

[Geliang Tang]

On Wed, Sep 28, 2022 at 01:02:07PM +0200, Paolo Abeni wrote:
> On Wed, 2022-09-28 at 17:48 +0800, Geliang Tang wrote:
> > To support redundant package schedulers more easily, this patch moves the
> > packet scheduler out of the dfrags loop in __mptcp_push_pending(), invoke
> > mptcp_sched_get_send() only once. 
> 
> I fear the above will make cause hitting HoL blocking [more]
> frequently/easily. I'm not sure if the simult_flows.sh self test will
> catch that, but you should see a measurably worse running time for such
> test - in non debug build, as the average of multiple runs.

Yes, simult_flows.sh self test failed in my tests. I guess this problem
also exists in "BPF redundant scheduler" v12, because it also uses the
same logic in __mptcp_push_pending(), move the packet scheduler out of
the dfrags loop.

> 
> I'm sorry, I can't see a feasible way out here :(
> 
> /P
> 

Re: [PATCH mptcp-next 1/4] mptcp: update __mptcp_push_pending

[Mat Martineau]

On Wed, 28 Sep 2022, Geliang Tang wrote:

> On Wed, Sep 28, 2022 at 01:02:07PM +0200, Paolo Abeni wrote:
>> On Wed, 2022-09-28 at 17:48 +0800, Geliang Tang wrote:
>>> To support redundant package schedulers more easily, this patch moves the
>>> packet scheduler out of the dfrags loop in __mptcp_push_pending(), invoke
>>> mptcp_sched_get_send() only once.
>>
>> I fear the above will make cause hitting HoL blocking [more]
>> frequently/easily. I'm not sure if the simult_flows.sh self test will
>> catch that, but you should see a measurably worse running time for such
>> test - in non debug build, as the average of multiple runs.
>
> Yes, simult_flows.sh self test failed in my tests. I guess this problem
> also exists in "BPF redundant scheduler" v12, because it also uses the
> same logic in __mptcp_push_pending(), move the packet scheduler out of
> the dfrags loop.
>

Hi Geliang -


Thanks for posting the __mptcp_push_pending() changes as a separate 
series, that's the main area of complexity in the BPF redundant scheduler 
series. I was trying to come up with some more detailed proposals for this 
part of the code, but it will be easier to discuss it in this 4-patch 
series.


We had talked about the need to change the __mptcp_push_pending() loops to 
support the redundant scheduler, since the existing structure and locking 
optimizations don't fit well with trying to send the same dfrags across 
multiple subflows. A simplified view of the existing code is this:

/* [1] Existing send loops */
For each dfrag:
 	While sends succeed:
 		Call the scheduler (selects subflow and msk->snd_burst)
 		Update subflow locks (push/release/acquire as needed)
 		Send the dfrag data with mptcp_sendmsg_frag()
 		Update dfrag->already_sent, msk->snd_nxt, msk->snd_burst
 	Update msk->first_pending
Push/release on final subflow


With the redundant scheduler, it's necessary to send each dfrag on 
multiple subflows. If the top-level loop is "For each dfrag", then 
redundant sends have to lock/unlock every subflow on every iteration of 
the inner loop.

Because of that, I proposed changing the outer loop to be based on the 
scheduler:


/* [2] Proposed send loops */
While the scheduler selects one or more subflows:
 	For each subflow:
 		Lock the subflow
 		For each pending dfrag:
 			Send the dfrag data with mptcp_sendmsg_frag()
 			Break if required by msk->snd_burst / etc
 		Push and release the subflow
 	Update dfrag metadata and msk->first_pending

>>
>> I'm sorry, I can't see a feasible way out here :(
>>

I'm still optimistic here :)

Whatever the outer loop is, I think we can still make basically the same 
sequence of calls to the subflow locks, mptcp_sendmsg_frag(), and 
tcp_push(). And fewer scheduler calls too! That would maintain the 
blest-like behavior Paolo implemented.

It seems to me that this v1 iteration of the patches is missing one 
important detail compared to the proposed pseudocode [2]: There's no outer 
loop to call the scheduler again after msk->snd_burst is exhausted. If 
this block of code is moved out of mptcp_subflow_get_send():

 	/* re-use last subflow, if the burst allow that */
 	if (msk->last_snd && msk->snd_burst > 0 &&
 	    sk_stream_memory_free(msk->last_snd) &&
 	    mptcp_subflow_active(mptcp_subflow_ctx(msk->last_snd))) {
 		mptcp_set_timeout(sk);
 		return msk->last_snd;
 	}

and those conditions are instead checked in the inner "For each pending 
dfrag" loop of my proposed pseudocode above, I think the single subflow 
case is feasible. Once that is working then redundant subflow support can 
be added in later patches.


--
Mat Martineau
Intel

[PATCH mptcp-next 2/4] mptcp: add do_push_pending helper

[Geliang Tang]

This patch moves the duplicate code from __mptcp_push_pending() and
__mptcp_subflow_push_pending() into a new helper function, named
__do_push_pending(). And simplify __mptcp_push_pending() by invoking
this helper.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c | 65 ++++++++++++++++++++++++--------------------
 1 file changed, 36 insertions(+), 29 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index fc972d56926e..6a20a000622f 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1491,12 +1491,6 @@ struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
 	return ssk;
 }
 
-static void mptcp_push_release(struct sock *ssk, struct mptcp_sendmsg_info *info)
-{
-	tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle, info->size_goal);
-	release_sock(ssk);
-}
-
 static void mptcp_update_post_push(struct mptcp_sock *msk,
 				   struct mptcp_data_frag *dfrag,
 				   u32 sent)
@@ -1528,43 +1522,29 @@ void mptcp_check_and_set_pending(struct sock *sk)
 		mptcp_sk(sk)->push_pending |= BIT(MPTCP_PUSH_PENDING);
 }
 
-void __mptcp_push_pending(struct sock *sk, unsigned int flags)
+static int __do_push_pending(struct sock *sk, struct sock *ssk,
+			     struct mptcp_sendmsg_info *info)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
-	struct mptcp_sendmsg_info info = {
-				.flags = flags,
-	};
-	bool do_check_data_fin = false;
 	struct mptcp_data_frag *dfrag;
-	struct sock *ssk;
-	int len;
-
-	ssk = mptcp_sched_get_send(msk);
-	if (!ssk)
-		goto out;
-
-	if (!mptcp_send_head(sk))
-		goto out;
-
-	lock_sock(ssk);
+	int len, copied = 0;
 
 	while ((dfrag = mptcp_send_head(sk))) {
-		info.sent = dfrag->already_sent;
-		info.limit = dfrag->data_len;
+		info->sent = dfrag->already_sent;
+		info->limit = dfrag->data_len;
 		len = dfrag->data_len - dfrag->already_sent;
 		while (len > 0) {
 			int ret = 0;
 
-			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
+			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, info);
 			if (ret <= 0) {
 				if (ret == -EAGAIN)
 					continue;
-				mptcp_push_release(ssk, &info);
 				goto out;
 			}
 
-			do_check_data_fin = true;
-			info.sent += ret;
+			info->sent += ret;
+			copied += ret;
 			len -= ret;
 
 			mptcp_update_post_push(msk, dfrag, ret);
@@ -1572,7 +1552,34 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
 		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
 	}
 
-	mptcp_push_release(ssk, &info);
+out:
+	if (copied) {
+		tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle,
+			 info->size_goal);
+	}
+
+	return copied;
+}
+
+void __mptcp_push_pending(struct sock *sk, unsigned int flags)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct mptcp_sendmsg_info info = {
+		.flags = flags,
+	};
+	int do_check_data_fin = 0;
+	struct sock *ssk;
+
+	ssk = mptcp_sched_get_send(msk);
+	if (!ssk)
+		goto out;
+
+	if (!mptcp_send_head(sk))
+		goto out;
+
+	lock_sock(ssk);
+	do_check_data_fin = __do_push_pending(sk, ssk, &info);
+	release_sock(ssk);
 
 out:
 	/* ensure the rtx timer is running */
-- 
2.35.3

[PATCH mptcp-next 3/4] mptcp: update __mptcp_subflow_push_pending

[Geliang Tang]

Move the packet scheduler out of the dfrags loop, invoke it only once in
__mptcp_subflow_push_pending().

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c | 36 ++++++++++++------------------------
 1 file changed, 12 insertions(+), 24 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 6a20a000622f..550fc375a7a6 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1598,7 +1598,15 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 	struct mptcp_data_frag *dfrag;
 	struct sock *xmit_ssk;
 	int len, copied = 0;
-	bool first = true;
+
+	xmit_ssk = mptcp_sched_get_send(mptcp_sk(sk));
+	if (!xmit_ssk)
+		goto out;
+	if (xmit_ssk != ssk) {
+		mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk),
+				       MPTCP_DELEGATE_SEND);
+		goto out;
+	}
 
 	info.flags = 0;
 	while ((dfrag = mptcp_send_head(sk))) {
@@ -1608,19 +1616,6 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 		while (len > 0) {
 			int ret = 0;
 
-			/* the caller already invoked the packet scheduler,
-			 * check for a different subflow usage only after
-			 * spooling the first chunk of data
-			 */
-			xmit_ssk = first ? ssk : mptcp_sched_get_send(mptcp_sk(sk));
-			if (!xmit_ssk)
-				goto out;
-			if (xmit_ssk != ssk) {
-				mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk),
-						       MPTCP_DELEGATE_SEND);
-				goto out;
-			}
-
 			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
 			if (ret <= 0)
 				goto out;
@@ -1628,7 +1623,6 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 			info.sent += ret;
 			copied += ret;
 			len -= ret;
-			first = false;
 
 			mptcp_update_post_push(msk, dfrag, ret);
 		}
@@ -3191,16 +3185,10 @@ void __mptcp_check_push(struct sock *sk, struct sock *ssk)
 	if (!mptcp_send_head(sk))
 		return;
 
-	if (!sock_owned_by_user(sk)) {
-		struct sock *xmit_ssk = mptcp_sched_get_send(mptcp_sk(sk));
-
-		if (xmit_ssk == ssk)
-			__mptcp_subflow_push_pending(sk, ssk);
-		else if (xmit_ssk)
-			mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk), MPTCP_DELEGATE_SEND);
-	} else {
+	if (!sock_owned_by_user(sk))
+		__mptcp_subflow_push_pending(sk, ssk);
+	else
 		__set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->cb_flags);
-	}
 }
 
 #define MPTCP_FLAGS_PROCESS_CTX_NEED (BIT(MPTCP_PUSH_PENDING) | \
-- 
2.35.3

[PATCH mptcp-next 4/4] mptcp: simplify __mptcp_subflow_push_pending

[Geliang Tang]

This patch simplifies __mptcp_subflow_push_pending() by invoking
__do_push_pending() helper.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c | 27 +++------------------------
 1 file changed, 3 insertions(+), 24 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 550fc375a7a6..779794f42137 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1593,11 +1593,11 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct mptcp_sendmsg_info info = {
+		.flags		= 0,
 		.data_lock_held = true,
 	};
-	struct mptcp_data_frag *dfrag;
 	struct sock *xmit_ssk;
-	int len, copied = 0;
+	int copied = 0;
 
 	xmit_ssk = mptcp_sched_get_send(mptcp_sk(sk));
 	if (!xmit_ssk)
@@ -1608,34 +1608,13 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 		goto out;
 	}
 
-	info.flags = 0;
-	while ((dfrag = mptcp_send_head(sk))) {
-		info.sent = dfrag->already_sent;
-		info.limit = dfrag->data_len;
-		len = dfrag->data_len - dfrag->already_sent;
-		while (len > 0) {
-			int ret = 0;
-
-			ret = mptcp_sendmsg_frag(sk, ssk, dfrag, &info);
-			if (ret <= 0)
-				goto out;
-
-			info.sent += ret;
-			copied += ret;
-			len -= ret;
-
-			mptcp_update_post_push(msk, dfrag, ret);
-		}
-		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
-	}
+	copied = __do_push_pending(sk, ssk, &info);
 
 out:
 	/* __mptcp_alloc_tx_skb could have released some wmem and we are
 	 * not going to flush it via release_sock()
 	 */
 	if (copied) {
-		tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
-			 info.size_goal);
 		if (!mptcp_timer_pending(sk))
 			mptcp_reset_timer(sk);
 
-- 
2.35.3

Re: mptcp: simplify __mptcp_subflow_push_pending: Tests Results

[MPTCP CI]

Hi Geliang,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal:
  - Unstable: 1 failed test(s): selftest_mptcp_join 🔴:
  - Task: https://cirrus-ci.com/task/5267113110667264
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/5267113110667264/summary/summary.txt

- KVM Validation: debug:
  - Success! ✅:
  - Task: https://cirrus-ci.com/task/6156566679257088
  - Summary: https://api.cirrus-ci.com/v1/artifact/task/6156566679257088/summary/summary.txt

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/9801ca9d6329


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)