The Disappointing Direction Of Linux Performance From 4.16 To 5.4 Kernels

The SQLite INSERT test improved significantly from Linux 4.16 to 4.17 and remained largely the same through Linux 5.3. But now with Linux 5.4 there appears to be a big pull-back in performance, at least for the EXT4 file-system on NVMe storage with this particular system. As always, the Phoronix Test Suite runs tests multiple times to rule out any noise....

When running eight copies of the SQLite test, sure enough, there was a big pull-back in performance on the current Linux 5.4 Git kernel that puts it in an even worse spot than Linux 4.16. This was surprising to us and previously didn't see this behavior and not due to mitigations so we'll be running more benchmarks looking at this change in performance.

Thankfully the I/O performance in Linux 5.4 isn't outright lower -- when running basic I/O tests with FIO the Linux 5.4 performance was either the same or slightly better.

The t-test1 memory allocation benchmark is one of the cases we have seen impacted over time as a result of all the different mitigations.