netdev - Re: [PATCH net-next] mptcp: Use 32-bit DATA

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Date:   Sat, 16 May 2020 13:51:26 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     cpaasch@...le.com
Cc:     kuba@...nel.org, netdev@...r.kernel.org, mptcp@...ts.01.org,
        pabeni@...hat.com, mathew.j.martineau@...ux.intel.com,
        matthieu.baerts@...sares.net
Subject: Re: [PATCH net-next] mptcp: Use 32-bit DATA_ACK when possible

From: Christoph Paasch <cpaasch@...le.com>
Date: Thu, 14 May 2020 08:53:03 -0700

> RFC8684 allows to send 32-bit DATA_ACKs as long as the peer is not
> sending 64-bit data-sequence numbers. The 64-bit DSN is only there for
> extreme scenarios when a very high throughput subflow is combined with a
> long-RTT subflow such that the high-throughput subflow wraps around the
> 32-bit sequence number space within an RTT of the high-RTT subflow.
> 
> It is thus a rare scenario and we should try to use the 32-bit DATA_ACK
> instead as long as possible. It allows to reduce the TCP-option overhead
> by 4 bytes, thus makes space for an additional SACK-block. It also makes
> tcpdumps much easier to read when the DSN and DATA_ACK are both either
> 32 or 64-bit.
> 
> Signed-off-by: Christoph Paasch <cpaasch@...le.com>

Applied, thanks.