Comment #3 on issue 301 by dorma...@rydia.net: link fails for GCC atomic functions
http://code.google.com/p/memcached/issues/detail?id=301
Take a look through the configure script, it's supposed to actually test and use the atomic call, and fail back if it fails.
The problem is that 32bit x86 doesn't have 16bit atomics, so they have to be detected and disabled. Except some versions of GCC (the one you have) claims to have them anyway, and it'll fail at runtime. 32bit is stuck with the mutex, but given how much memory you're limited to, I doubt you'd ever notice the performance drop. It just won't be hugely faster than .11.
I have no idea why setting march=i686 makes it work right, and I don't have your OS to test on :/ Since that's all pretty old legacy stuff, we might have to insist you compile with your workaround.
I'd consider a patch to the autocrap if it doesn't degrade any of our supported platforms.
