Linux 5.0 To Linux 5.9 Kernel Benchmarking Was A Bumpy Ride With New Regressions

For the most part the performance was fairly flat though not too surprising given the AMD EPYC 7702 / Zen 2 CPUs have good support going back to late Linux 4.x kernels. Though in some areas there are performance changes worth noting.

In particular with I/O, the kernels were on a slower trend for some workloads...

One of the most surprising results though was seeing Linux 5.9's random read performance with the modern IO_uring interface get demolished... While the performance had been on a nice upward trend since Linux 5.4 and succeeding kernel releases, with Linux 5.9-rc4 on the same FIO test configuration the performance plummeted to much lower performance than even when IO_uring was introduced in Linux 5.1.

Notably though with the same FIO but using Linux AIO instead of IO_uring, Linux 5.9 didn't regress.

Fortunately, the sequential read performance with IO_uring was stead. But the IO_uring random read drop is bisected and explained later on in this article, so let's move on to some of the other tested workloads...