[FR] Easy attaching perf from within the library

[DenisYaroshevskiy]

Is your feature request related to a problem? Please describe.

Sometimes benchmarks have a heavy setup which affects counters/recordings.
It would be nice to easily skip heavy initialization when using perf.

Describe the solution you'd like

folly benchmarks has --bm_perf_args which will start perf after doing a first iteration of a benchmark.
Running the first iteration of the benchmark allows to skip initialization of statics.

For example in folly benchmarks I can run --bm_perf_args=record or --bm_perf_args=stat.

That works ok but isn't very generic. Maybe you know something more generic?

Describe alternatives you've considered
It is possible to do this through external tools but is very annoying.