linux-kernel - RE: [PATCH linux-next 1/3] selftests: net: udpgso_bench

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Date:   Tue, 18 Apr 2023 09:01:17 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Yang Yang <yang.yang29@....com.cn>, willemdebruijn.kernel@...il.com
Cc:     davem@...emloft.net, edumazet@...gle.com, jiang.xuexin@....com.cn,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
        pabeni@...hat.com, shuah@...nel.org, xu.xin16@....com.cn,
        yang.yang29@....com.cn, zhang.yunkai@....com.cn
Subject: RE: [PATCH linux-next 1/3] selftests: net: udpgso_bench_rx: Fix
 verifty exceptions

Yang Yang wrote:
> > Why are you running two senders concurrently? The test is not intended
> > to handle that case.
> 
> Sorry for the inaccuracy of the description here, these two commands,
> i.e. with or without GSO, cause the problem. The same goes for patch 2/3.
> The problem is easily reproducible in the latest kernel, QEMU environment, E1000.
> 
> bash# udpgso_bench_tx -l 4 -4 -D "$DST" 
> udpgso_bench_tx: write: Connection refused
> bash# udpgso_bench_rx -4 -G -S 1472 -v
> udpgso_bench_rx: data[1472]: len 17664, a(97) != q(113)
> 
> bash# udpgso_bench_tx -l 4 -4 -D "$DST" -S 0
> udpgso_bench_tx: sendmsg: Connection refused
> bash# udpgso_bench_rx -4 -G -S 1472 -v
> udpgso_bench_rx: data[61824]: len 64768, a(97) != w(119)

I still don't follow: are you running the tx and rx commands
sequentially or in parallel? On different (virtual) hosts?
 
> In one test, the verification data is printed as follows:
> abcd...xyz
> ...
> abcd...xyz
> abcd...opabcd...xyz
> 
> This is because the sender intercepts from the buf at a certain length,
> which is not aligned according to 26 bytes, and multiple packets are
> merged. The verification of the receiving end needs to be performed
> after splitting.

The 26 bytes is a reference to the pattern printed by the test, which
iterates over A-Z.

Is your point that each individual segment starts at A, so that a test
for pattern {ABC..Z}+ only matches if the segments size is a multiple
of 26, else a the pattern will have discontinuities?