In addition to the points other people raised, "simply" removing the GIL by changing the current reference-counting GC to do atomic reference updates will also

In addition to the points other people raised, "simply" removing the GIL by changing the current reference-counting GC to do atomic reference updates will also substantially reduce single threaded performance; there was a PyCon talk about that. https://www.youtube.com/watch?v=P3AyI_u66Bw https://www.youtube.com/watch?v=P3AyI_u66Bw See also Swift for another language whose implementation has performance issues caused by ubiquitous atomic reference counting.