netdev - Re: [PATCH] selftests: net: udpgso_bench_tx: Introduce exponential back-off retries

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Date:   Mon, 30 Jan 2023 09:26:05 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Willem de Bruijn <willemb@...gle.com>,
        Andrei Gherzan <andrei.gherzan@...onical.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: net: udpgso_bench_tx: Introduce exponential
 back-off retries

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@...onical.com> wrote:
> > 
> > The tx and rx test programs are used in a couple of test scripts including
> > "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 ready to
> > accept socket connections. This racing bug could fail the test with at
> > least one of the following:
> > 
> > ./udpgso_bench_tx: connect: Connection refused
> > ./udpgso_bench_tx: sendmsg: Connection refused
> > ./udpgso_bench_tx: write: Connection refused
> > 
> > This change addresses this by adding routines that retry the socket
> > operations with an exponential back off algorithm from 100ms to 2s.
> > 
> > Fixes: 3a687bef148d ("selftests: udp gso benchmark")
> > Signed-off-by: Andrei Gherzan <andrei.gherzan@...onical.com>
> 
> Synchronizing the two processes is indeed tricky.
> 
> 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