DragonFlyBSD's Meltdown Fix Causing More Slowdowns Than Linux

At least in most of the CPU benchmarks, the performance hasn't changed.

The Python PyBench performance regressed with these latest patches.

The PHP performance measured by PHPBench also dropped with machdep.isolated_user_pmap enabled on both systems.

The I/O performance remains the most dramatic slowdowns as a result of this Meltdown vulnerability fix. But unlike our bare metal Linux numbers with the same test profiles, in some of the other workloads we are also seeing more noticeable performance degregading from GraphicsMagick to Python to PHP. Hopefully though as DragonFlyBSD 5.1 continues to be developed there will be more performance optimizations in store. We also have yet to see how DragonFlyBSD plans to address the Spectre vulnerability. As covered already, the other BSDs are also still working on their fixes.