Re: [PATCH v3 net-next 0/7] mptcp: implement TCP_NOTSENT_LOWAT support

[Mat Martineau <martineau@kernel.org>]

On Fri, 16 Feb 2024, Paolo Abeni wrote:

> Patch 6/7 does the magic, all the others are minor cleanup and fix of
> buglet exposed by such feature. I'll push a paired pktdrill test.
>
> Note that this relies on the existing accounting for snd_nxt. As I
> stated such accounting is not 110% accurate as it tracks the most recent
> sequence number queued to any subflow, and not the actual sequence
> number sent on the wire.
>
> I experimented a lot trying to implement the latter and in the end it
> proved to be both "too complex" and "not necessary".
>
> The complexity raises from the need for additional lock and a lot of
> refactory to introduce such protection without adding significant
> overhead. Additionally, snd_nxt is currenly used and exposed with the
> current semantic both eBPF and the internal packet scheduling.
> Introducing a different tracking will still require us to keep the old
> one.
>
> More interesting, a more accurate tracking could be not strictly
> necessary: as the MPTCP protocol enqueues data to the subflows only up
> the available send window, any enqueue data is sent on the wire
> instantly, without any blocking operation short of a drop in the tx path
> at the nft or TC layer.
>
> The individual patches changelog carry the gory details.
>

v3 of the series LGTM, thanks Paolo.

Matthieu note that this series is split between mptcp-net and mptcp-next:

> Still sending a single series to outline the functional requirements,
> even if the first 3 patches could land on mptcp-net directly.
>

Reviewed-by: Mat Martineau <martineau@kernel.org>


> v2 -> v3:
>  - typo in patch 1/7
>  - dropped unused code in patch 3/7
>  - dropped duplicate code in patch 6/7
>
> v1 -> v2:
>  - clarifiy commit message in patch 1/7
>  - fix possible wake-up bug in patch 6/7
>
> *** BLURB HERE ***
>
> Paolo Abeni (7):
>  mptcp: push at DSS boundaries
>  mptcp: fix snd_wnd initialization for passive socket
>  mptcp: fix potential wake-up event loss
>  mptcp: cleanup writer wake-up
>  mptcp: avoid some duplicate code in socket option handling
>  mptcp: implement TCP_NOTSENT_LOWAT support.
>  mptcp: cleanup SOL_TCP handling
>
> net/mptcp/protocol.c | 57 ++++++++++++++++++++++++-----------
> net/mptcp/protocol.h | 51 ++++++++++++++++++++++---------
> net/mptcp/sockopt.c  | 71 ++++++++++++++++++++------------------------
> 3 files changed, 108 insertions(+), 71 deletions(-)
>
> -- 
> 2.43.0
>
>
>