http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58642
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Weird, can't reproduce. /tmp/ttt 8 taskset -c 0-3 /tmp/ttt 4 ldd /tmp/ttt | grep libgomp libgomp.so.1 => /usr/src/gomp-4.0/obj/x86_64-unknown-linux-gnu/libgomp/.libs/libgomp.so.1 (0x00007fda5e2e8000) strace /tmp/ttt 2>&1 | grep affinity sched_getaffinity(30384, 8, {ff}) = 8 taskset -c 0-3 strace /tmp/ttt 2>&1 | grep affinity sched_getaffinity(30389, 8, {f}) = 8 Do you have the default linux build (i.e. --enable-linux-futex), or one without that (that doesn't honor affinity)?