Strange gaps between `threadpool_map` calls?
See http://astro.dur.ac.uk/~pdraper/swift/threadpool-plots/eagle_25_4-1/poolstep10r.html.
There is actually no computation between the calls to runner_do_unskip_mapper
, scheduler_rewait_mapper
, and scheduler_enqueue_mapper
, but at least 1ms between calls.