And yet empirically there is a 20-40% slowdown: http://mail.python.org/pipermail/python-ideas/2009-November/006599.html http://mail.python.org/pipermail/python

And yet empirically there is a 20-40% slowdown: http://mail.python.org/pipermail/python-ideas/2009-November/006599.html http://mail.python.org/pipermail/python-ideas/2009-November/... The message is not too specific; is this on an SMP machine? Are these multi-threaded tests? Given the previous message I cited, I would expect the single-CPU, single-threaded case to be unaffected by making incref and decref atomic.