Re: [PATCH v8] tcp: move seq_to_tap update to when frame is queued

[Stefano Brivio <sbrivio@redhat.com>]

On Tue,  4 Jun 2024 14:29:08 -0400
Jon Maloy <jmaloy@redhat.com> wrote:

> commit a469fc393fa1 ("tcp, tap: Don't increase tap-side sequence counter for dropped frames")
> delayed update of conn->seq_to_tap until the moment the corresponding
> frame has been successfully pushed out. This has the advantage that we
> immediately can make a new attempt to transmit a frame after a failed
> trasnmit, rather than waiting for the peer to later discover a gap and
> trigger the fast retransmit mechanism to solve the problem.
> 
> This approach has turned out to cause a problem with spurious sequence
> number updates during peer-initiated retransmits, and we have realized
> it may not be the best way to solve the above issue.
> 
> We now restore the previous method, by updating the said field at the
> moment a frame is added to the outqueue. To retain the advantage of
> having a quick re-attempt based on local failure detection, we now scan
> through the part of the outqueue that had do be dropped, and restore the
> sequence counter for each affected connection to the most appropriate
> value.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> 
> ---
> v2: - Re-spun loop in tcp_revert_seq() and some other changes based on
>         feedback from Stefano Brivio.
>     - Added paranoid test to avoid that seq_to_tap becomes lower than
>       seq_ack_from_tap.
> 
> v3: - Identical to v2. Called v3 because it was embedded in a series
>       with that version.
> 
> v4: - In tcp_revert_seq(), we read the sequence number from the TCP
>       header instead of keeping a copy in struct tcp_buf_seq_update.
>     - Since the only remaining field in struct tcp_buf_seq_update is
>       a pointer to struct tcp_tap_conn, we eliminate the struct
>       altogether, and make the tcp6/tcp3_buf_seq_update arrays into
>       arrays of said pointer.
>     - Removed 'paranoid' test in tcp_revert_seq. If it happens, it
>       is not fatal, and will be caught by other code anyway.
>     - Separated from the series again.
> 
> v5: - Changed way to index array within tcp_revert_seq()
> 
> v6-v7: No changes.
> 
> v8: Fixed missing indexing of tcp4/6_frame_conns array in
>     tcp_payload_flush().

Applied, thanks.

-- 
Stefano