On https://developer.mozilla.org/en-US/docs/Mozilla/Benchmarking I am collecting a set of reasons why profiled builds may be substantially slower than release builds. It would be really nice if the gecko profiler could store enough information in the profiles to tell whether any of these things were in effect, and if so, prominently display that in the performance tab and in Cleopatra.
For example, GC poisoning is a substantial slowdown. Some people claim async stacks are. Debug builds obviously are. I suspect a lot of profiling is done with inappropriate builds.
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