HPC cluster. Which Linux distribution to choose and how to achieve performance?

Question

linux

There is an HPC cluster that runs on an old Debian 7 distribution.
The task was to update the distribution to a modern one. Debian 9/CentOS 7 etc.
It would seem that nothing complicated, but the following problem arose. The benchmark built into the used computing software gives worse results on new distributions (in some places up to 10%) than on the old one.
Actually questions:
1) Are the new kernels so bad, or is something turned off by default and must be forced to turn on?
2) Has anyone done testing and tuning for high performance computing and can share their experience?