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Subject: Re: [OMPI users] Performance question about OpenMPI and MVAPICH2 on IB
From: Gerry Creager (gerry.creager_at_[hidden])
Date: 2009-08-06 19:11:08


Craig,

Let me look at your script, if you'd like... I may be able to help
there. I've also been seeing some "interesting results for WRF on
OpenMPI, and we may want to see if we're taking complimentary approaches...

gerry

Craig Tierney wrote:
> A followup....
>
> Part of problem was affinity. I had written a script to do processor
> and memory affinity (which works fine with MVAPICH2). It is an
> idea that I got from TACC. However, the script didn't seem to
> work correctly with OpenMPI (or I still have bugs).
>
> Setting --mca mpi_paffinity_alone 1 made things better. However,
> the performance is still not as good:
>
> Cores Mvapich2 Openmpi
> ---------------------------
> 8 17.3 17.3
> 16 31.7 31.5
> 32 62.9 62.8
> 64 110.8 108.0
> 128 219.2 201.4
> 256 384.5 342.7
> 512 687.2 537.6
>
> The performance number is GFlops (so larger is better).
>
> The first few numbers show that the executable is the right
> speed. I verified that IB is being used by using OMB and
> checking latency and bandwidth. Those numbers are what I
> expect (3GB/s, 1.5mu/s for QDR).
>
> However, the Openmpi version is not scaling as well. Any
> ideas on why that might be the case?
>
> Thanks,
> Craig
>
>
> Craig Tierney wrote:
>> I am running openmpi-1.3.3 on my cluster which is using
>> OFED-1.4.1 for Infiniband support. I am comparing performance
>> between this version of OpenMPI and Mvapich2, and seeing a
>> very large difference in performance.
>>
>> The code I am testing is WRF v3.0.1. I am running the
>> 12km benchmark.
>>
>> The two builds are the exact same codes and configuration
>> files. All I did different was use modules to switch versions
>> of MPI, and recompiled the code.
>>
>> Performance:
>>
>> Cores Mvapich2 Openmpi
>> ---------------------------
>> 8 17.3 13.9
>> 16 31.7 25.9
>> 32 62.9 51.6
>> 64 110.8 92.8
>> 128 219.2 189.4
>> 256 384.5 317.8
>> 512 687.2 516.7
>>
>> The performance number is GFlops (so larger is better).
>>
>> I am calling openmpi as:
>>
>> /opt/openmpi/1.3.3-intel/bin/mpirun --mca plm_rsh_disable_qrsh 1 --mca btl openib,sm,self \
>> -machinefile /tmp/6026489.1.qntest.q/machines -x LD_LIBRARY_PATH -np $NSLOTS /home/ctierney/bin/noaa_affinity ./wrf.exe
>>
>> So,
>>
>> Is this expected? Are some common sense optimizations to use?
>> Is there a way to verify that I am really using the IB? When
>> I try:
>>
>> -mca bta ^tcp,openib,sm,self
>>
>> I get the errors:
>> --------------------------------------------------------------------------
>> No available btl components were found!
>>
>> This means that there are no components of this type installed on your
>> system or all the components reported that they could not be used.
>>
>> This is a fatal error; your MPI process is likely to abort. Check the
>> output of the "ompi_info" command and ensure that components of this
>> type are available on your system. You may also wish to check the
>> value of the "component_path" MCA parameter and ensure that it has at
>> least one directory that contains valid MCA components.
>> --------------------------------------------------------------------------
>>
>> But ompi_info is telling me that I have openib support:
>>
>> MCA btl: openib (MCA v2.0, API v2.0, Component v1.3.3)
>>
>> Note, I did rebuild OFED and put it in a different directory
>> and did not rebuild OpenMPI. However, since ompi_info isn't
>> complaining and the libraries are available, I am thinking that
>> is isn't a problem. I could be wrong.
>>
>> Thanks,
>> Craig
>
>

-- 
Gerry Creager -- gerry.creager_at_[hidden]
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
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