[go-nuts] How does pprof work under the hood?

I am looking for a simple explanation of how the pprof library works. So
far, this is what I have learned:

    - It runs a stop-the-world sampler. In other words, it periodically
    stops the program being profiled to collect information.
    - It uses gperftools <http://code.google.com/p/gperftools/> underneath.

Besides a general overview, here are some specific questions I would like
answered:

    - Is pprof an "event based profiler
    <https://en.wikipedia.org/wiki/Profiling_(computer_programming)#Event-based_profilers>"
    or "instrumentation profiler
    <https://en.wikipedia.org/wiki/Profiling_(computer_programming)#Instrumentation>".
    From what I understand, these profilers modify the way a program runs and
    collect samples via those modifications
    - At what 'level' in the OS does pprof profile? Does it profile the
    kernal like SystemTap <https://sourceware.org/systemtap/> or perf
    <https://perf.wiki.kernel.org/index.php/Main_Page>?
    - Is pprof safe to run on a high-traffic production server?

I am asking this question to reason about the overhead introduced by using
pprof on a Go server.