=Global definition=
https://docs.google.com/document/d/1WfJ-2ytYtZnyafbd_PJbr7S_OjVqg8s18HJszk7uQEM/edit

=perf & flamegraph example =
https://talawah.io/blog/extreme-http-performance-tuning-one-point-two-million/#flame-graph-generation