What's the best way of achieving a parallel infinite Loop?

Stephen Toub has a post about Implementing Parallel While with Parallel.ForEach.

If you (really) want something infinite then you want it on as few cores a possible. None of the Parallel.For___ would be a good choice.

What you (probably) need is a separate Thread or a Task created with the LongRunning option.

And then make it wait on a semaphore, or as a last resort call Sleep() as often as possible.