After upgrade to 1.6.5, I got "AIO is not supported on this machine!" in the error.log.
after check the difference between 1.5.10 and 1.6.5, it's issue of 1.6.5, not sure it's done on purpose.
for examples, source http/httpsession.h,
in 1.5.10,
#include <edio/aioeventhandler.h>
in 1.6.5...