------- Comment From [email protected] 2020-03-20 06:01 EDT-------
Hi,

first let me get to your questions regarding the kernel.

As you already guessed, this was an upstream (fedora) kernel and the latest 
version at the time we pursued the issue. That is also the answer to why we did 
not use the stable 5.4.
However, the problem appeared already with older kernel versions since the 
commit named above was introduced with 4.18.

Now getting to the problem.
Before the code change stated above, striding RQ was used with ConnectX-4 
devices. By introducing the commit, the default RQ was set to "legacy RQ" for 
ConnectX-4 devices as the comment in the commit already indicates, "this 
implies that ConnectX-4 LX now uses legacy RQ by default".

As our performance tests showed for z14 and z15 it is beneficial to use
striding RQ with ConnectX-4 (RoCE Express 2(.1)).

That is why we ask to switch the default for ConnectX-4 back to striding RQ 
when using a z14/z15. This can be done by calling the following command:
ethtool --set-priv-flags DEVNAME rx_striding_rq on

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https://bugs.launchpad.net/bugs/1868113

Title:
  [Ubuntu 20.04]  Striding RQ as Default for ConnectX-4

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