Running performance test on aarch64, I get:

[root@host kernel-tests]# ./runtests.sh -t performance
Test suite called with performance
../scripts/gnu-os: unable to guess system type

This script, last modified 2004-08-18, has failed to recognize
the operating system you are using. It is advised that you
...

And a bunch of other lines.

As far as I can see, here http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=con we can find a newer version. Placing it in performance/lmbench3/scripts/ overwriting the other one, it is able to identify the system.