Linux 5.11 Is Regressing Hard For AMD Performance With Schedutil
Written by Michael Larabel in Software on 25 December 2020. Page 3 of 6. 32 Comments

Where things got a bit interesting and what kicked off my original Linux 5.11 AMD performance examination were the PostgreSQL results...

To some surprise, the improvement with PostgreSQL looks at least in part unrelated to the Schedutil change as some nice uplift was also seen under the performance governor on Linux 5.11 too.

The performance isn't uniformly lower on Linux 5.11 when using Schedutil but found to affect roughly half or more of the workloads tried thus far. When looking at the peak CPU frequency being achieved across all of the benchmarks being carried out, when using Linux 5.11 with Schedutil saw the peak frequency averaging out to be around 100MHz lower than on Linux 5.10 with Schedutil.

But long story short, indeed on AMD EPYC seeing lower performance in a number of different workloads only when using the Schedutil governor. This seems to jive with the initial hypothesis that these varying regressions stem from the AMD frequency invariance support merged last week into the Linux 5.11 cycle. Switching over to the performance governor doesn't show such drops to the performance. It also looks like the PostgreSQL improvement on EPYC that initially got us excited for Linux 5.11 is from a separate change this cycle and will be looked at more.

Now let's look at the desktop situation...

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