Message-ID: <a762638b06684cd63d212d1ce9f65236a08b78b1.camel@redhat.com>
Subject: Re: [PATCH] selftests: net: udpgso_bench_tx: Introduce exponential
 back-off retries
From:   Paolo Abeni <pabeni@redhat.com>
To:     Willem de Bruijn <willemb@google.com>,
        Andrei Gherzan <andrei.gherzan@canonical.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Shuah Khan <shuah@kernel.org>, netdev@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Mon, 30 Jan 2023 09:26:05 +0100
In-Reply-To: <CA+FuTSewU6bjYLsyLzZ1Yne=6YBPDJZ=U1mZc+6cJVdr06BhiQ@mail.gmail.com>
References: <20230127181625.286546-1-andrei.gherzan@canonical.com>
         <CA+FuTSewU6bjYLsyLzZ1Yne=6YBPDJZ=U1mZc+6cJVdr06BhiQ@mail.gmail.com>
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On Fri, 2023-01-27 at 17:03 -0500, Willem de Bruijn wrote:
> On Fri, Jan 27, 2023 at 1:16 PM Andrei Gherzan
> <andrei.gherzan@canonical.com> wrote:
> >=20
> > The tx and rx test programs are used in a couple of test scripts includ=
ing
> > "udpgro_bench.sh". Taking this as an example, when the rx/tx programs
> > are invoked subsequently, there is a chance that the rx one is not read=
y to
> > accept socket connections. This racing bug could fail the test with at
> > least one of the following:
> >=20
> > ./udpgso_bench_tx: connect: Connection refused
> > ./udpgso_bench_tx: sendmsg: Connection refused
> > ./udpgso_bench_tx: write: Connection refused
> >=20
> > This change addresses this by adding routines that retry the socket
> > operations with an exponential back off algorithm from 100ms to 2s.
> >=20
> > Fixes: 3a687bef148d ("selftests: udp gso benchmark")
> > Signed-off-by: Andrei Gherzan <andrei.gherzan@canonical.com>
>=20
> Synchronizing the two processes is indeed tricky.
>=20
> Perhaps more robust is opening an initial TCP connection, with
> SO_RCVTIMEO to bound the waiting time. That covers all tests in one
> go.

Another option would be waiting for the listener(tcp)/receiver(udp)
socket to show up in 'ss' output before firing-up the client - quite
alike what mptcp self-tests are doing.

Cheers,

Paolo