Re: [PATCH mptcp-next v3 4/5] mptcp: update __mptcp_subflow_push_pending

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

On Fri, 30 Sep 2022, Geliang Tang wrote:

> 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>

Hi Geliang -

I think the __mptcp_push_pending() changes are looking good. Some changes 
are needed here for __mptcp_subflow_push_pending().

> ---
> net/mptcp/protocol.c | 44 ++++++++++++++++++++------------------------
> 1 file changed, 20 insertions(+), 24 deletions(-)
>
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index dc5e03a616b3..8e67c149bbab 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -1589,7 +1589,15 @@ 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(msk);
> +	if (!xmit_ssk)
> +		goto out;
> +	if (xmit_ssk != ssk) {
> +		mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk),
> +				       MPTCP_DELEGATE_SEND);
> +		goto out;
> +	}

There's no need to delegate before the first __do_push_pending(). In the 
existing code, the first send skips the scheduler call and tries to send 
on the selected ssk (the one that's the last arg to the function).

The existing code then calls the scheduler after each 
mptcp_sendmsg_frag(), and if the scheduler chooses a different xmit_ssk 
then mptcp_subflow_delegate() is called and it does the 'goto out'.

In other words, this function also needs a loop like 
__mptcp_push_pending() to call the scheduler multiple times.


- Mat

>
> 	info.flags = 0;
> 	while ((dfrag = mptcp_send_head(sk))) {
> @@ -1599,19 +1607,6 @@ 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(msk);
> -			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;
> @@ -1619,11 +1614,18 @@ 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);
> 		}
> 		WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
> +
> +		if (msk->snd_burst > 0 &&
> +		    sk_stream_memory_free(ssk) &&
> +		    mptcp_subflow_active(mptcp_subflow_ctx(ssk))) {
> +			mptcp_set_timeout(sk);
> +		} else {
> +			break;
> +		}
> 	}
>
> out:
> @@ -3182,16 +3184,10 @@ 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
>
>
>

--
Mat Martineau
Intel