A pair of workqueue improvements

Userspace can already pin unbound workqueues via the usual taskset mechanism. What problem is the new locality mechanism therefore trying to solve? In particular, applications that allocate an unbound workqueue for a particular task are already able to pin the kworker on the same core where the task runs. kworkers with a unique CPU affinity are potentially dedicated to the one task, and userspace can therefore also manage their priority with chrt. As always, all these benefits depend on the ability of developers to reason about what affinities and priorities should be.