Going back to the start of December with the Linux 5.5 merge window we have encountered several significant performance regressions. Over the weeks since we’ve reproduced the behavior on both Intel and AMD systems along with large and small CPUs. Following some holiday weekend bisecting fun, here is the cause at least partially for the Linux 5.5 slowdowns.
On a number of different systems this month we’ve seen several regressions in real-world workloads like NPB and Parboil, PostgreSQL, Memcached, RocksDB, and also synthetic tests like the Hackbench scheduler benchmark. Worth noting, as to be explained, all these systems were running Ubuntu Linux.