[melchebo]

Just read the paper, it's explained. Or read the presentation, it uses pictures.

Basically they run R, a single threaded statistics tool which is setup to hog a core, and in some other cgroup a wildly multithreaded tool. If you have a NUMA system (check with `lstopo`) then it's possible that the scheduler thinks the many tasks in one domain of cores is balanced with just R on one core of another domain. Meaning you can have several (ex: 7 out of 8) cores idle. It has to do with the way hierarchical rebalancing is coded, and that their 8x 8-core AMD machine has a deep hierarchy.