Implement systematic profiling

[unzvfu]

Useful in general obviously, but also for performance regressions. Some relevant links:

• https://danluu.com/perf-tracing/
  • https://github.com/RRZE-HPC/likwid
  • https://stackoverflow.com/questions/26021337/what-is-iaca-and-how-do-i-use-it
  • https://stackoverflow.com/questions/8389648/how-do-i-achieve-the-theoretical-maximum-of-4-flops-per-cycle?rq=1
  • https://perf.wiki.kernel.org/index.php/Tutorial#Sampling_with_perf_record
• https://danluu.com/assembly-intrinsics/
• https://danluu.com/new-cpu-features/