The Performance Impact Of Spectre Mitigation On POWER9

Written by Michael Larabel in Software on 11 November 2018. Page 1 of 4. 16 Comments

Over the past year we have looked extensively at the performance impact of Spectre mitigations on x86_64 CPUs but now with having the Raptor Talos II in our labs, here are some benchmarks to see the performance impact of IBM's varying levels of Spectre mitigation for POWER9.

By default, Raptor Computing Systems ships their system in the safest mode of providing full kernel and user-space protection against Spectre Variant Two. But by editing a file from the OpenBMC environment it's possible to control the Spectre protections on their libre hardware. Besides the full/user protection against Spectre there is also kernel-only protection that is more akin to the protection found on x86_64 CPUs. Additionally, there is the ability to completely disable the protection for yielding the greatest performance (or what would be considered standard pre-2018) but leaving your hardware vulnerable to Spectre. More details on controlling the Spectre protections on Talos II hardware can be found via the Wiki.

This weekend are some benchmarks for reference of the Talos II Secure Workstation with dual 22-core POWER9 CPUs when tested in the default mode of kernel/user protection, kernel protection only, and then no protection at all for seeing how the performance compares -- just as we have done many times over the past year for Intel and AMD CPUs too.

These reference benchmarks were done via the Phoronix Test Suite. If you want to see how your own Linux system(s) compare to the performance of this fully open-source system with libre firmware in its various Spectre configurations, simply run phoronix-test-suite benchmark 1811098-SK-TALOSIIDU15.

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