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Subject: Re: [OMPI users] Some Newbie questions
From: Ashika Umanga Umagiliya (aumanga_at_[hidden])
Date: 2009-06-29 21:48:46

Thanks all for the answers,

I am parallelizing tomography algorithm which takes about 5 hours using
single processor.
I want to gain full performance and should reduce the computational
time as short as possible.
I was wondering the SSh/RSH launcher could be a performance issue?(I
am just guessing)
What kind of software/middleware I should use to solve the
network/communication overhead.
(different launchers ,may be Sun Grid Engine,XGrid ? ) I am runing
Debian/Lenny and since the project is academic I want to use OSS ..

Best Regards,

Jeff Squyres wrote:
> On Jun 29, 2009, at 2:19 AM, vipin kumar wrote:
>> Q. Since I am using TCP/Ethernet I guess that MPI uses SSH/RSH to
>> communicate between peers.
>> Ans. May be you are right. I don't know exactly how peers communicate
>> in MPI environment, but I can say for sure that OpenMPI uses rsh/ssh
>> as one of the available launchers.
> Open MPI uses two different mechanisms for launching individual MPI
> processes vs. MPI communications. rsh/ssh is one of the options that
> Open MPI can use for launching MPI processes, but we don't keep those
> channels open and don't use them for MPI communications. Individual,
> new TCP sockets are opened for MPI_SEND / MPI_RECV (etc.) traffic.
> These sockets are not encrypted (like ssh connections would be).
>> Q. And for that, each peer should have the copy of the application
>> right?
>> Ans. Absolutely correct. But If you don't want to copy binaries
>> manually you should use "--preload-binary" option. OpenMPI will copy
>> the executables in remote nodes before launching processes, and will
>> delete when job gets done.
>> It is almost always good to use latest version. "--preload-binary"
>> option may be absent in old versions.
> It is new in the 1.3 series; it did not exist in the 1.2 series.