Interesting, the log_num_mtt and log_mtts_per_seg params where not set.
Setting them to utilise 2*8G of my RAM resulted in no change to the stalls or run time ie; (19,3) (20,2) (21,1) or (6,16). 
In all cases, OpenIB runs in twice the time it takes TCP,except if I push the small message max to 64K and force short messages.  Then the openib times are the same as TCP and no faster.

I'ms till at a loss as to why...


From: Paul Kapinos <kapinos@rz.rwth-aachen.de>
To: Randolph Pullen <randolph_pullen@yahoo.com.au>; Open MPI Users <users@open-mpi.org>
Sent: Tuesday, 28 August 2012 6:13 PM
Subject: Re: [OMPI users] Infiniband performance Problem and stalling

Randolph,
after reading this:

On 08/28/12 04:26, Randolph Pullen wrote:
> - On occasions it seems to stall indefinately, waiting on a single receive.

... I would make a blind guess: are you aware about IB card parameters for registered memory?
http://www.open-mpi.org/faq/?category=openfabrics#ib-low-reg-mem

"Waiting forever" for a single operation is one of symptoms of the problem especially in 1.5.3.


best,
Paul

P.S. the lower performance with 'big' chinks is known phenomenon, cf.
http://www.scl.ameslab.gov/netpipe/
(image on bottom of the page). But the chunk size of 64k is fairly small




-- Dipl.-Inform. Paul Kapinos  -  High Performance Computing,
RWTH Aachen University, Center for Computing and Communication
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