I can confirm that this bug is still present in Python 2.4.1 (and
probably later versions) on AIX 5.2 and 5.3.

When HAVE_BROKEN_POSIX_SEMAPHORES is not defined at compile time, Python
will spend a lot of time in sem_wait, usually when acessing files.
The problem does not always happen as it seems to depend on the type of
file system in use.

In my programm running for 3m30s, Python would call about 400000 time
sem_wait and spend about 2mins waiting. When Python is compiled with
HAVE_BROKEN_POSIX_SEMAPHORES, the same programm will only take 1m30s.

I attach a patch which solves the problem.