The Spectre/Meltdown Performance Impact On Linux 4.20, Decimating Benchmarks With New STIBP Overhead

The slowdown in Python performance was found to be caused by STIBP.

Fortunately, not all Python workloads are affected as much as the PyBench results.

PHP performance is now affected by these mitigations due to STIBP where as with earlier Spectre/Meltdown work the performance of this popular server language was mostly unchanged.

The V-RAY renderer was only to be found slightly affected by STIBP, less so than Blender.

With some of these tests being impaired measurably by the STIBP code that landed in Linux 4.20, we can only hope that optimizations are soon on the way for either tuning the STIBP heuristics or other changes to provide cross-HT protection while affecting the performance less.