netdev - [net PATCH 0/2] tcp: Address issues with ECT0 not being set in DCTCP packets

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Date:   Thu, 19 Nov 2020 13:23:43 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, daniel@...earbox.net, kafai@...com,
        kernel-team@...com, edumazet@...gle.com, brakmo@...com,
        alexanderduyck@...com, weiwan@...gle.com
Subject: [net PATCH 0/2] tcp: Address issues with ECT0 not being set in DCTCP
 packets

This patch set is meant to address issues seen with SYN/ACK packets not
containing the ECT0 bit when DCTCP is configured as the congestion control
algorithm for a TCP socket.

A simple test using "tcpdump" and "test_progs -t bpf_tcp_ca" makes the
issue obvious. Looking at the packets will result in the SYN/ACK packet
with an ECT0 bit that does not match the other packets for the flow when
the congestion control agorithm is switch from the default. So for example
going from non-DCTCP to a DCTCP congestion control algorithm we will see
the SYN/ACK IPV6 header will not have ECT0 set while the other packets in
the flow will. Likewise if we switch from a default of DCTCP to cubic we
will see the ECT0 bit set in the SYN/ACK while the other packets in the
flow will not.

---

Alexander Duyck (2):
      tcp: Allow full IP tos/IPv6 tclass to be reflected in L3 header
      tcp: Set INET_ECN_xmit configuration in tcp_reinit_congestion_control

 net/ipv4/tcp_cong.c | 5 +++++
 1 file changed, 5 insertions(+)

--