I'll have to re-look at the details of credit2 about load balance and
migration between CPUs/runqueues but it looks like we need to have
something allowing us to honour pinning/affinity _within_ the same
runqueue, anyway, don't we? I mean, even if you implement per-L2
runqueues, that would still span more than one CPU, and the user may
well want to pin a vCPU to only one (or in general a subset) of them.