Re: [PATCH mptcp-next v2 1/4] mptcp: update __mptcp_push_pending

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

On Thu, 29 Sep 2022, 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. And update the socket locks
> correspondingly.
>
> Signed-off-by: Geliang Tang <geliang.tang@suse.com>
> ---
> net/mptcp/protocol.c | 50 ++++++++++++++++++--------------------------
> 1 file changed, 20 insertions(+), 30 deletions(-)
>
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 7ca21915b3d1..37a252a3f05b 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -1417,14 +1417,6 @@ struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
> 	u64 linger_time;
> 	long tout = 0;
>
> -	/* 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;
> -	}
> -

With msk->last_snd not used here any more, it seems like it can be 
removed.

> 	/* pick the subflow with the lower wmem/wspace ratio */
> 	for (i = 0; i < SSK_MODE_MAX; ++i) {
> 		send_info[i].ssk = NULL;
> @@ -1530,15 +1522,21 @@ 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;
> +
> +	lock_sock(ssk);
> +
> 	while ((dfrag = mptcp_send_head(sk))) {
> 		info.sent = dfrag->already_sent;
> 		info.limit = dfrag->data_len;
> @@ -1546,24 +1544,6 @@ 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)
> @@ -1579,11 +1559,21 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
> 			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;
> +		}
> 	}
>
> -	/* at this point we held the socket lock for the last subflow we used */
> -	if (ssk)
> -		mptcp_push_release(ssk, &info);
> +	if (do_check_data_fin) {
> +		tcp_push(ssk, 0, info.mss_now, tcp_sk(ssk)->nonagle,
> +			 info.size_goal);
> +	}
> +	release_sock(ssk);
>
> out:
> 	/* ensure the rtx timer is running */
> -- 
> 2.35.3
>
>
>

--
Mat Martineau
Intel