Copied from tl;dr: (Emphases in the original)<p>> This blog post will show how a fix for XFree86 and linuxthreads ended up causing a major threading regression <i>about 7 years</i> after the fix was created.<p>> The regression was in `pthread_create`. Thread creation performed very slowly as the number of threads in a process increased. <i>This bug is present on CentOS 5.3 (and earlier) and other linux distros as well.</i><p>Actually, while it merits a (fine) blog post, it is far from being <i>the</i> craziest as the original post title suggests. But what I find really important is surely the following paragraph:<p>> It is also very possible that this bug impacted research done before <i>August 15, 2008</i> (in the best case because Linux distro releases are slow) on building high performance threaded applications.<p>Research is hard since you may be affected with every possible cause unknown to you.