It looks like Bert’s patch adjusted two ldconfig calls; the first one was in a BSD-specific branch. Was this intended? Only the second call (default “else:” branch) seems applicable to AIX.

Perhaps the performance is improved now that the popen() shell calls have been replaced with more direct subprocess.Popen() calls; see revision a09ae70f3489 and Issue 22636. If the 300 ms slowdown was due to the shell, that should no longer be a problem.

But if the slowdown is say inherent in fork(), I am not sure it is worth adding the proposed os.path.exists() check. Either try a way of spawning a child process without fork(), like Issue 20104. Or avoid calling find_library() in the first place, like I suggested at <https://bugs.python.org/issue11063#msg264151>.