Thread affinities

[hguo]

It would be great to add a feature to automatically set thread affinities. Otherwise we have to manually call sched_setaffinity() on some systems..

[mrzv]

Hi Hanqi, I'd be happy to add this to DIY, but I don't know enough about it to know the right way to do it. If you have a specific way in mind, let me know. This may also be related to #23.