[kolbusa]

In my experience, EIGEN's threadpool is decent. But OpenMP (edit: I mean Intel's implementation donated to LLVM) is often faster especially if threads are allowed to be affinitized to HW processors. Another promise of OpenMP that is not made by various threadpools is cooperative execution; in threadpools tasks are usually independent.

However, if any part of an app uses affinitized threads, the whole app needs to be using the same thread pool, as otherwise perf will go down. In this regard, OpenMP is less composable.