5.x was extremely buggy and unstable. It got usable around only after 5.4 release. 5.x wasn't just the removal of Giant Lock, but also: - GEOM - Kernel Sched

5.x was extremely buggy and unstable. It got usable around only after 5.4 release. 5.x wasn't just the removal of Giant Lock, but also: - GEOM - Kernel Scheduled Entities There weren't any reasons to switch from 4.x to 5.x until 5.x got stable. Even with Giant Lock given the hardware at the time (Pentium with hyper threading) it wasn't that bad.