LuaJIT Profiler

This Minetest mod lets you use LuaJIT's builtin profiler. This profiler is good for pinpointing expensive parts of mod code.

How to Use

• Add the mod to the secure.trusted_mods list.
• Enable the mod.
• In-game start the profiler with /jitprofiler_start 1 <filename>. The profiling data will be written to <worldpath>/jitprofiles/<filename>.
• Collect data for a while.
• Stop profiling with /jitprofiler_stop or by exiting the world.
• Download FlameGraph if you haven't done so.
• Create a flame graph SVG with ./flamegraph.pl <worldpath>/jitprofiles/<filename> > graph.svg.
• Open the SVG with your browser or another viewing program.
• The top level of each stack snapshot will be "C", "G", "I", "J", or "N", representing C code, garbage collection, interpreter, JIT compilation, or compiled code, respectively.

Issues

• This mod can cause the game to hang somehow. Most of the profiling data collected before the hang is saved.
• Sometimes a lot of C code execution is reported in suspicious places. I think this represents time taken by the Minetest engine, but I don't know why the profiler thinks the code is executed inside a Lua function.
• Using this mod with Mesecons luacontrollers can cause crashes for some reason.