The AMD Zen 2 / Zen 3 Performance Fix For Linux 5.11 Has Landed

Just in time for the expected Linux 5.11 stable release on Sunday, the AMD frequency invariance performance regression I've been noting and writing about since Christmas day has been resolved with the previously covered fix having been merged today.

That regression affecting Zen 2 / Zen 3 laptops and desktops through servers stems from the introduction of AMD frequency invariance that is new this kernel cycle and quickly showed itself if using the Schedutil (scheduler utilization) governor while the likes of the performance governor were unaffected. The change only affects AMD Zen 2 / Zen 3 hardware due to the frequency invariance support depending upon ACPI CPPC data, which isn't found on prior generations of AMD processors. Intel has had their own frequency invariance implementation for the Linux kernel going back a while.

As noted last week, addressing the regression ultimately is done by a change to CPUFreq. Those two CPUFreq patches were merged today to Linux 5.11 Git: cpufreq: ACPI: Extend frequency tables to cover boost frequencies and cpufreq: ACPI: Update arch scale-invariance max perf ratio if CPPC is not there. The change is outlined via the commit message below.

The work landed with pm-5.11-rc8 pull that was merged to mainline a few minutes ago. Phew, Was getting nervous this important change was going to be too late for 5.11.0.

See this article from last week for the now expected performance improvements to find with Linux 5.11: After A Bumpy Cycle, AMD Performance Will Shine Brighter On Linux 5.11. The change often not only addressed the regression but Linux 5.11 is now for many workloads delivering superior performance to Linux 5.10 and prior. I have some more benchmarks in the next few days.