From: Jakub Kicinski <kuba@kernel.org>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org,
daniel@iogearbox.net, kafai@fb.com, kernel-team@fb.com,
edumazet@google.com, brakmo@fb.com, alexanderduyck@fb.com
Subject: Re: [net PATCH] tcp: Set ECT0 bit in tos/tclass for synack when BPF needs ECN
Date: Tue, 24 Nov 2020 14:14:55 -0800 [thread overview]
Message-ID: <20201124141455.432f73cc@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <160593039663.2604.1374502006916871573.stgit@localhost.localdomain>
On Fri, 20 Nov 2020 19:47:44 -0800 Alexander Duyck wrote:
> From: Alexander Duyck <alexanderduyck@fb.com>
>
> When a BPF program is used to select between a type of TCP congestion
> control algorithm that uses either ECN or not there is a case where the
> synack for the frame was coming up without the ECT0 bit set. A bit of
> research found that this was due to the final socket being configured to
> dctcp while the listener socket was staying in cubic.
>
> To reproduce it all that is needed is to monitor TCP traffic while running
> the sample bpf program "samples/bpf/tcp_cong_kern.c". What is observed,
> assuming tcp_dctcp module is loaded or compiled in and the traffic matches
> the rules in the sample file, is that for all frames with the exception of
> the synack the ECT0 bit is set.
>
> To address that it is necessary to make one additional call to
> tcp_bpf_ca_needs_ecn using the request socket and then use the output of
> that to set the ECT0 bit for the tos/tclass of the packet.
>
> Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control")
> Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Applied, thank you!
prev parent reply other threads:[~2020-11-24 22:15 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-21 3:47 [net PATCH] tcp: Set ECT0 bit in tos/tclass for synack when BPF needs ECN Alexander Duyck
2020-11-24 22:14 ` Jakub Kicinski [this message]
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