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From: George Bosilca (bosilca_at_[hidden])
Date: 2006-06-13 11:02:34


Well, if there is no reuse in the application buffers, then the 2
approaches will give the same results. Because of our pipelined
protocol it might happens that we will reach even better performance
for large messages. If there is buffer reuse, the mpich-gm approach
will lead to better performances, but to more pinned memory. In fact,
the main problem is not the memory, but the memory hooks (like the
ones in the lib c) that need to be take care by the MPI library in
order to notice when one of the already registered memory location is
released (freed) by the user.

At least with our approach the user have the choice. By default we
turn them off, but it is really easy for any user to turn on the
pinned memory registration, if he/she think that his MPI application
require it. There is a paper to be published this year at Euro PVM/
MPI which shows that for some *real* applications (like the NAS
benchmarks) there is no real difference. But it is definitively for
the ping-pong benchmark ...

   Thanks,
     george.

On Jun 13, 2006, at 10:38 AM, Brock Palen wrote:

> Ill provide new numbers soon with the --mac mpi_leave_pinned 1
> I'm currious how does this affect real application performace? This
> ofcourse is a synthetic test using NetPipe. For regular apps that
> move decent amounts of data but want low latency more.
> Will that be affected?
>
> Brock Palen
> Center for Advanced Computing
> brockp_at_[hidden]
> (734)936-1985
>
>
> On Jun 13, 2006, at 10:26 AM, George Bosilca wrote:
>
>> Unlike mpich-gm, Open MPI does not keep the memory pinned by default.
>> You can force this by ading the "--mca mpi_leave_pinned 1" to your
>> mpirun command or by adding it into the Open MPI configuration file
>> as specified on the FAQ (section performance). I think that should be
>> the main reason what you're seeing a such degradation of
>> performances.
>>
>> If this does not solve your problem, can you please provide the new
>> performance as well as the output of the command "ompi_info --param
>> all all".
>>
>> Thanks,
>> george.
>>
>> On Jun 13, 2006, at 10:01 AM, Brock Palen wrote:
>>
>>> I ran a test using openmpi-1.0.2 on OSX vs mpich-1.2.6 from
>>> mryicom and i get lacking results from OMPI,
>>> at point point there is a small drop in bandwidth for both MPI
>>> libs, but open mpi does not recover like mpich, and further on you
>>> see a decreese in bandwidth for OMPI on gm.
>>>
>>> I have attached in png and the outputs from the test (there are
>>> two for OMPI )
>>> <bwMyrinet.png>
>>> <bwOMPI.o1969>
>>> <bwOMPI.o1979>
>>> <bwMPICH.o1978>
>>>
>>> Brock Palen
>>> Center for Advanced Computing
>>> brockp_at_[hidden]
>>> (734)936-1985
>>>
>>>
>>> _______________________________________________
>>> users mailing list
>>> users_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>
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