How to use #flamegraphs for #performance #profiling
https://runbooks.gitlab.com/tutorials/how_to_use_flamegraphs_for_perf_profiling/
Off-CPU Analysis - by Brendan Gregg:
https://www.brendangregg.com/offcpuanalysis.html
- On-CPU: where threads are spending time running on-CPU
- Off-CPU: where time is spent waiting while blocked on I/O, locks, timers, paging/swapping, etc.