AMD EPYC 7F72 Performance On A Linux FSGSBASE-Patched Kernel

Slated for Linux 5.9 is finally mainlining the FSGSBASE patches that have been floating around the kernel mailing list for years. Testing last week showed the tentative x86/fsgsbase patches helping Intel Xeon Linux performance but with AMD also supporting this instruction set extension going back to Bulldozer, how is it looking on the likes of AMD? Here are some benchmarks.

In continuation of the Intel benchmarks last week and our various articles in recent times of the FSGSBASE wiring up for the Linux kernel, this article is quite straight-forward in providing some metrics for the AMD impact. For this round of testing an AMD EPYC 7F72 server was used. Assuming the upstream developers don't have second thoughts and not send the support in for Linux 5.9, I'll be back with more desktop/server tests when the 5.9 cycle gets underway in August.

Like the Intel testing, when building a fresh Linux kernel build from the x86/fsgsbase branch, the AMD EPYC 7F72 tests were done with FSGSBASE enabled and then again when booting the same kernel with "nofsgsbase" for disabling the FSGSBASE support. Confirmation of FSGSBASE being disabled on a patched kernel can be found by then seeing "fsgsbase" removed from /proc/cpuinfo. There is also a test case in the Linux kernel source tree for verifying FSGSBASE instruction support.