[OMPI devel] sm BTL flow management

[Eugene Loh]

I have a fix for ticket 1944 working, but the broader problem is 
unpleasant.  E.g., let's say we have zillions of uncountered Bcasts or 
something.  Say, the root is repeatedly emitting sends, but never 
polling its in-coming FIFO.  Return fragments will be accumulating, the 
FIFO will be congested, pending-send queues on peer processes will be 
growing, etc.  The code now handles this (by growing the pending-send 
queues and eventually draining them, pre-1.3.2 we would also have 
handled this by growing the FIFO and using up the shared memory), but 
the whole thing is disturbing.  E.g., queues might drain only when the 
root reaches MPI_Finalize.  (Okay, unclear to me what sort of real 
application would have communications only from one process going out.)

So, is this (one-way communications, e.g., repeated Bcasts) pathological 
and not worth worrying about.  Or, are other solutions worth 
considering?  E.g., I'd like to have a sending process run 
mca_btl_sm_component_progress occasionally, even if it is successfully 
completing its sends.