Heisenprofiling, verb: wasting unnecessary time trying to figure out why your inner loops are still running slowly after optimization, only to realize that it's because the profiler hooks are slowing it down...
Years ago, with insufficient experience, I was trying to debug a device-driver problem. I used printfs. Stupid.
Eventually I created an in-memory array, updated that with integer data which corresponded to information I wanted, and that was "fast enough" to expose the issue.
Many years later, on a Connection Machine, we discovered that asking for the current day/date would bring all processors to a screeching halt while the system propagated the correct date/time to every processor. Also while trying to profile behavior and performance.
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Eventually I created an in-memory array, updated that with integer data which corresponded to information I wanted, and that was "fast enough" to expose the issue.
Many years later, on a Connection Machine, we discovered that asking for the current day/date would bring all processors to a screeching halt while the system propagated the correct date/time to every processor. Also while trying to profile behavior and performance.
It's not easy.