The Current Intel Coffee Lake Mitigation Performance Impact With Linux 5.9

Of the many new features in Linux 5.9 with its debut set for this weekend, one of the performance-related changes is Intel FSGSBASE support finally being mainlined. A half-decade after the Linux patches first appeared for this feature present in Intel CPUs going back to Ivy Bridge, the mainline kernel is now patched for this feature that can help out I/O and other context switching heavy workloads. Given many of the same workloads were negatively impacted by the CPU security mitigations of recent years, here is a look at the current mitigated vs. unmitigated performance difference on the Linux 5.9 kernel with an Intel Core i9 9900K CPU for reference on how the mitigation impact is on recent versions of the Linux kernel.