3 ms·

It'd cost a little more than that, wouldn't it? I thought once the counters were configured there was a (potentially tiny?) overhead to any type of forward prog

• nkurz 9y ago
  if you say it barely exists I'll be using far more of perf and other things like it... I'll back Brendan and claim that using hardware CPU counters on modern server processors is basically free. They are internal to the processor, and essentially don't utilize any resources shared with program execution. Maybe you could contrive a case where they cause faster thermal throttling, but I haven't seen it. For a simple count of events that is started and stopped at context switches (and when you are counting fewer events than available hardware counters) I'd be surprised if you even saw 1% overhead. If you are trying to multiplex many more events than you have physical counters, the overhead of "reprogramming" the counters might cost you single digit overhead. If you are trying to save all stack traces, record all branches, or monitor all memory accesses you can manage to create a more significant slowdown, but even then you can usually lower this something acceptable by sampling. So yes --- you probably should be using perf far more! Or VTune, or likwid (https://github.com/RRZE-HPC/likwid https://github.com/RRZE-HPC/likwid).