The Performance Impact Of Spectre Mitigation On POWER9

With the PHP and Python performance when having the kernel-only protection there is virtually no performance impact but in the safest (and default) method of kernel+user protection the performance is about halved.

The socket performance was impacted a bit by these Spectre mitigations, but not as much as we've seen from the x86_64 mitigations.

The semaphores performance hit was less than what we've seen on the x86_64 CPU space as well... I'll likely do some Intel vs. AMD vs. POWER9 Spectre relative performance benchmarks shortly.

The Hackbench Linux kernel scheduler benchmark showed a modest performance pullback.

When having full kernel+user protection as shipped by default, the time to build the Linux kernel on POWER9 did slowdown by about five seconds.

There is a small I/O performance hit, similar to with Intel/AMD CPUs.