I am profiling #GNOME Shell (MASSIVE thanks to #fedora enabling frame pointers for all packages in 38 making this possible) and noticed clock_gettime() taking up a huge chunk. Turns out I hit
https://bugzilla.kernel.org/show_bug.cgi?id=202525: many #AMD laptops are forced to use a very slow clock source (HPET instead of TSC). #Lenovo fixed it with a BIOS update for some laptops but not mine. Kernel param tsc=reliable results in big speedups (up to 30% in browser benchmarks) but unsure if it impacts stability :/