To be explicit, I was skeptical because I believed that GIL removal requires adding overhead for managing memory access. Having dug a bit deeper into it that seems confirmed. The proposed GIL removal strategy _is slower for single-threaded code_ like other solutions before it. It turns out the reported performance increase was the result of orthogonal performance improvements overshadowing the overhead of GIL removal.
Put another way, if the performance improvements were upstreamed without removing the GIL the resulting performance increase would be ~20% instead of just ~10%. Which is what Guido was getting at in the quote I cited. Assuming the benchmarks to be true for the moment, this means that removing the GIL on this PoC branch is a 10% performance hit to single-threaded workloads.
Put another way, if the performance improvements were upstreamed without removing the GIL the resulting performance increase would be ~20% instead of just ~10%. Which is what Guido was getting at in the quote I cited. Assuming the benchmarks to be true for the moment, this means that removing the GIL on this PoC branch is a 10% performance hit to single-threaded workloads.