We've heard about this a few times now (Ning with the fattree, Misbah with the dragonfly model / MPI replay program, and potentially Misbah/Caitlin with "awesim" runs) - something is causing performance regressions (resulting in less ROSS efficiency) when using model-net vs direct ROSS in optimistic mode.

It's unclear why this is happening for the time being. model-net imposes two extra events (sched-new, sched-next) per model_net_event call, the first of which is a remote from the client (the original "packet event" that the client used to directly send is now a self-event). I would imagine there to be some degree of overhead for this, but nothing that would significantly affect the rollback rate / ROSS efficiency...

We should keep this in the back of our minds while we are working on other things.