[mvapich-discuss] Buffer size of unexpected receive queue, is there a way to increase the buffer?

[Craig Tierney]

I am trying to figure out a way to increase the
unexpected receive queue, if it is even possible
or necessary.

I have code that looks a bit like:

for i=0,npes-1
   msgsize=Some function to determine how much data (even 0) should be sent to another PE
   mpi_send(send to process i, msgsize)
   if (msgsize > 0)
     mpi_send(send to process i, data of msgsize bytes)
done

for i=0,npes-1
   mpi_recv(receive from procss i, msgsize)
   if (msgsize > 0)
     mpi_recv(receive from process i, data of msgsize bytes)
done

On my job with 864 cores, the code is blocking in here.
I believe that since the receives are not posted, that I
am most likely hitting some internal buffer limits.  This
code works on other systems, but they have had to tweak
internal buffer sizes to get it to work.

I cannot change the code in any way.  So I am looking
for how the size of the unexpected receive queue is set
and if/how it can be changed.

Thanks,
Craig


-- 
Craig Tierney (craig.tierney at noaa.gov)