netdev - Re: [PATCH linux-next v2] selftests: net: udpgso_bench_tx: Add test for IP fragmentation of UDP packets

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Date:   Fri, 3 Mar 2023 19:00:45 +0800 (CST)
From:   <yang.yang29@....com.cn>
To:     <willemdebruijn.kernel@...il.com>
Cc:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <shuah@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <zhang.yunkai@....com.cn>, <xu.xin16@....com.cn>,
        <jiang.xuexin@....com.cn>
Subject: Re: [PATCH linux-next v2] selftests: net: udpgso_bench_tx: Add test for IP fragmentation of UDP packets

> Did you actually observe a difference in behavior with this change?

The test of UDP only cares about sending, and does not much need to
consider the problem of PMTU, we configure it to IP_PMTUDISC_DONT.
    IP_PMTUDISC_DONT: turn off pmtu detection.
    IP_PMTUDISC_OMIT: the same as DONT, but in some scenarios, DF will
be ignored. I did not construct such a scene, presumably when forwarding.
Any way, in this test, is the same as DONT.

We have a question, what is the point of this test if it is not compared to
UDP GSO and IP fragmentation. No user or tool will segment in user mode,
UDP GSO should compare performance with IP fragmentation.