The Performance Impact Of Spectre Mitigation On POWER9

The Cython performance was very noticeably impacted by the kernel+user protection.

While in the simple C-written AOBench renderer, having full protection only slowed down that benchmark by a few seconds.

The ray-tracing performance also slowed down by a few seconds with the full protection.

The full protection impacted the LLVM build times by a very small amount.

In the Stockfish chess benchmark having full Spectre protection slowed down its performance by about 5%. Though in these tests that are simply CPU heavy, on the x86_64 side we haven't seen much deviation in those numbers from Spectre mitigations.