In that test it is expected that lots of time is spent in TimeRemaining, but looks like nsRFPService::ReduceTimePrecisionImpl is adding quite a bit overhead there.
Bug 1655683 Comment 4 Edit History
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In that test it is expected that lots of time is spent in TimeRemaining, but looks like nsRFPService::ReduceTimePrecisionImpl is adding quite a bit overhead there. Is it RandomMidpoint calls which are slow? They are using a lock(!) in this super hot code path.