Test amount of data movement between workers

[Carreau]

dask/dask#6491 try to introduce broadcasting tricks for zeros/ones/full which (should) decrease the amount of communications between workers.
dask/dask#6343 test that "sizeof" give the base size instead of the full size.

Would a test in distributed that data-transfer is minimal be worth it in distributed ? And how would I do that ?

[mrocklin]

I think that workers have something like an _outgoing_transfer_log and _incoming_transfer_log (not exact names). So a gen_cluster test that used scatter, followed by a task on another machine using the workers= keyword in both cases that then checked ._outgoing_transfer_log would probably work.

x = c.submit(make_array, workers=[a.address])
y = c.submit(inc, x, workers=[b.address])
# look at a._outgoing_transfer_log