linux-kernel - Re: [PATCH bpf-next] tools/testing/selftests/bpf/test_tc

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Message-ID: <CAD1qLz0UwaFsk3ZnQ9e5RG1XvJ2i=7FJhtf_9AB6KVZ1fbEh3w@mail.gmail.com>
Date: Tue, 3 Dec 2024 09:23:51 -0800
From: Marco Leogrande <leogrande@...gle.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>, 
	Mykola Lysenko <mykolal@...com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	"Alessandro Carminati (Red Hat)" <alessandro.carminati@...il.com>, willemb@...gle.com, zhuyifei@...gle.com, 
	bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] tools/testing/selftests/bpf/test_tc_tunnel.sh:
 Fix wait for server bind

On Mon, Dec 2, 2024 at 4:15 PM Stanislav Fomichev <stfomichev@...il.com> wrote:
> Do you see this failing in your CI or in the BPF CI?

I see this failing in our internal CI, in around 1% to 2% of the CI runs.

> It seems ok
> to add wait_for_port here, but the likelihood of the issue seems
> minuscule. There is a bunch of ip/tc/etc calls between this
> server_listen and the next client_connect (and I'd be surprised to hear
> that netcat is still not listening by the time we reach next
> client_connect).

I'm surprised as well, and I've not found a good correlation with the
root cause of the delayed server start, besides generic "slowness".

You also make a good point - by calling wait_for_port this early we
"waste" the opportunity to run the other ip commands in parallel in
the meantime.
I had considered moving this wait down, just before the next
client_connect, but I concluded it might be less readable since it
would be so distant from the server_listen it pairs with. But I can
make that change if it seems better.