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

Besides the FIO IO_uring random read performance tanking on Linux 5.9, the other big surprise was seeing the Apache HTTPD performance being stressed concurrently with the Siege benchmark tanking on Linux 5.9! Like damn, it drops like a rock on Linux 5.9 as of RC4 now half-way through the cycle... This Apache regression is unrelated to the IO_uring Linux 5.9 drop and is bisected and documented in this article.

For the most part out of dozens of tests benchmarked across the past ten kernel series, overall the performance as tested on the AMD EPYC 7702 server was in good shape. The two big surprises in being major active performance drops on Linux 5.9 were around FIO with the IO_uring I/O interface's random read performance dropping and the Apache web server when stressed via Siege on the localhost seeing a major fall in the number of transactions per second being obtained. So then with this 64-core AMD EPYC server and the Phoronix Test Suite it was onwards to bisecting to see the culprits for why Linux 5.9 is doing poorly in these areas.

Those wanting to see all of the many Linux 5.0 to 5.9 kernel benchmarks in full can do so via this OpenBenchmarking.org result file.