Some time ago I stumbled upon this Hacker News discussion on how disable Spectre mitigation.
(For what Meltdown and Spectre is, refer to this article on 2018)
It is sad to say but my Intel NUC centrino was slowed down a lot by these mitigation, and the same faith is shared by old Intel server. Disabling it on Linux and Windows has a very huge improvements.
On windows this small utility was very effective to get back my CPU time