[mpich-discuss] Installation on Blue Gene/Q

[Latham, Robert J.]

On Wed, 2017-04-19 at 13:58 +0200, pramod kumbhar wrote:
> Hi Rob,
> 
> Is this already installed/avaialble on MIRA? I would like to try this
> to check some mpi i/o hints.

Yes, there are several versions available:

manual progress optimized:
/projects/aurora_app/mpich3-ch4-ofi/install/gnu/bin
 
auto progress optimized:
/projects/aurora_app/mpich3-ch4-ofi/install-auto/gnu/bin
 
manual progress debug:
/projects/aurora_app/mpich3-ch4-ofi/install/gnu.debug/bin
 
auto progress debug:
/projects/aurora_app/mpich3-ch4-ofi/install-auto/gnu.debug/bin

There are some performance considerations (both positive and negative)
to consider:

Current performance improvements versus [IBM's vendor-supplied MPICH]:

1.) Pt2pt latency - better than 2x speedup for small messages, large
ones with few ranks-per-node less so due to detriment #2  listed below.

2.) RMA latency - exponentially better for small messages, then becomes
gradually even for large messages in the case of put and get.

Current performance detriments versus [IBM's vendor-supplied MPICH]:

1.) No optimized collectives -- all collectives are pt2pt algorithms in
MPICH CH4.  There is a plan to develop optimized collectives via OFI
triggered operations but that work wouldn't begin until the April-May
timeframe at the earliest.  There is also a plan to make optimized
pt2pt collectives available sooner.

2.) Only 1 rget injection fifo utilized per rank to pt2pt communication
--- pami can utilize up all 11 to maximize internode bandwidth, you
would mainly see this have an impact if you are running < 8 ranks per
node and passing large messages.

==rob
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