The Speculative Execution Impact For A 4-Core POWER9 Blackbird Desktop
Overall there tends to be a generally small but noticeable performance hit from these mitigations but not nearly as significant as the Intel performance costs.
If looking at the geometric mean, the kernel-only protections performed basically the same as the unmitigated results at a high level. The default kernel+user protections meanwhile yielded about an 8% hit to the performance, much lower than the ~18% we're usually seeing on Intel CPUs. Coming up soon I'll have an Intel/AMD/POWER9/ARM mitigation impact comparison but for this article just wanted to get some numbers out there now on this POWER9 4-core / 16-thread system for those wondering about its status.
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