nix/doc/manual/rl-next/eval-profiler.md

synopsis	prs
Add stack sampling evaluation profiler	13220

Nix evaluator now supports stack sampling evaluation profiling via --eval-profiler flamegraph setting. It collects collapsed call stack information to output file specified by --eval-profile-file (nix.profile by default) in a format directly consumable by flamegraph.pl and compatible tools like speedscope. Sampling frequency can be configured via --eval-profiler-frequency (99 Hz by default).

Unlike existing --trace-function-calls this profiler includes the name of the function being called when it's available.