In the OMP Runtime we have a helper thread. My customers are asking where this thread is bound (or is it bound?) when using KMP_AFFINITY and a proclist. To make it simple, assume the proclist is 1,2,3,4. And OMP_NUM_THREADS=4. Pretty obvious where the worker threads get bound. What about the helper? Empirically on a HSW Cray XC-40 the customer is reporting seeing the helper bound to proc 2. Which surprised me. I would have thought proc 1. OR is it that the helper doesn't bind and floats within the proclist?
They are worried about how much 'noise' or interference one gets from this helper thread.