It's unclear to me if the author is saying that the global mutex for unwinding the stack interferes with the non-exception-throwing code paths, or are they just

It's unclear to me if the author is saying that the global mutex for unwinding the stack interferes with the non-exception-throwing code paths, or are they just saying that the exceptions themselves bottleneck and are so inefficient that this becomes a significant impact on overall throughput? It does seem like at least in theory it should be possible to create a non-locking / blocking exception unwinder, if there is no actual contention between the threads. If that can be done then it seems like the solution should be to do that rather than abandon a whole language feature. This is a bit like the Python GIL question. I would say if the language spec means you have to have a "GIL" in any context in a high performance language like C++ then it ought to be addressed at the spec level.