Just FYI, I commented out the usleep() in your test program and have been running your: seq 64 | xargs -n1 -P64 /bin/sh -c 'while ./a.out; do : ; done' test, and it's been running flawlessly for 2 hours on my T4. This is with Linus's current tree. I'll fire up my T3 later and try to reproduce it there.