Antoine, can you share the code for your benchmarks which show performance improvements when framing is enabled? I am seeing the same 10-15% slowdown even when pickling stuff to pure Python objects: ### Without the patch ./python -m timeit -r 50 -s "import pickle, _pyio; f = _pyio.BytesIO(); x = list(range(1000))" "pickle.dump(x, f, protocol=4)" 10000 loops, best of 50: 28.5 usec per loop ### With the patch ./python -m timeit -r 50 -s "import pickle, _pyio; f = _pyio.BytesIO(); x = list(range(1000))" "pickle.dump(x, f, protocol=4)" 10000 loops, best of 50: 32.9 usec per loop