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Subject: Re: [OMPI users] OpenMPI Run-Time "Freedom" Question
From: Tim Prince (n8tm_at_[hidden])
Date: 2010-08-12 21:28:09


On 8/12/2010 6:04 PM, Michael E. Thomadakis wrote:
> On 08/12/10 18:59, Tim Prince wrote:
>> On 8/12/2010 3:27 PM, Ralph Castain wrote:
>>> Ick - talk about confusing! I suppose there must be -some- rational
>>> reason why someone would want to do this, but I can't imagine what
>>> it would be....
>>>
>>> I'm no expert on compiler vs lib confusion, but some of my own
>>> experience would say that this is a bad idea regardless of whether
>>> or not OMPI is involved. Compiler version interoperability is
>>> usually questionable, depending upon how far apart the rev levels are.
>>>
>>> Only answer I can offer is that you would have to try it. It will
>>> undoubtedly be a case-by-case basis: some combinations might work,
>>> others might fail.
>>>
>>>
>>> On Aug 12, 2010, at 3:53 PM, Michael E. Thomadakis wrote:
>>>
>>>> Hello OpenMPI,
>>>>
>>>> we have deployed OpenMPI 1.4.1 and 1.4.2 on our Intel Nehalem
>>>> cluster using Intel compilers V 11.1.059 and 11.1.072 respectively,
>>>> and one user has the following request:
>>>>
>>>> Can we build OpenMPI version say O.1 against Intel compilers
>>>> version say I.1 but then built an application with OpenMPI O.1 BUT
>>>> then use a DIFFERENT Intel compiler version say I.2 to built and
>>>> run this MPI application?
>>>>
>>>> I suggested to him to 1) simply try to built and run the
>>>> application with O.1 but use Intel compilers version I.X whatever
>>>> this X is and see if it has any issues.
>>>>
>>>> OR 2) If the above does not work, I would build OpenMPI O.1 against
>>>> Intel version I.X so he can use THIS combination for his
>>>> hypothetical application.
>>>>
>>>> He insists that I build OpenMPI O.1 with some version of Intel
>>>> compilers I.Y but then at run time he would like to use *different*
>>>> Intel run time libs at will I.Z <> I.X.
>>>>
>>>> Can you provide me with a suggestion for a sane solution to this ? :-)
>>>>
>>>> Best regards
>>>>
>>>> Michael
>> Guessing at what is meant here, if you build MPI with a given version
>> of Intel compilers, it ought to work when the application is built
>> with a similar or more recent Intel compiler, or when the run-time
>> LD_LIBRARY_PATH refers to a similar or newer library (within reason).
>> There are similar constraints on glibc version. "Within reason"
>> works over a more restricted range when C++ is involved. Note that
>> the Intel linux compilers link to the gcc and glibc libraries as well
>> as those which come with the compiler, and the MPI could be built
>> with a combination of gcc and ifort to work with icc or gcc and
>> ifort. gfortran and ifort libraries, however, are incompatible,
>> except that libgomp calls can be supported by libiomp5.
>> The "rational" use I can see is that an application programmer would
>> likely wish to test a range of compilers without rebuilding MPI.
>> Intel documentation says there is forward compatibility testing of
>> libraries, at least to the extent that a build made with 10.1 would
>> work with 11.1 libraries.
>> The most recent Intel library compatibility break was between MKL 9
>> and 10.
>>
>
> Dear Tim, I offered to provide myself the combination of OMPI+ Intel
> compilers so that application can use it in stable fashion. When I
> inquired about this application so I can look into this I was told
> that "there is NO application yet (!) that fails but just in case it
> fails ..." I was asked to hack into the OMPI building process to let
> OMPI use one run-time but then the MPI application using this OMPI ...
> use another!
>
>
> Thanks for the information on this. We indeed use Intel Compiler set
> 11.1.XXX + OMPI 1.4.1 and 1.4.2.
>
> The basic motive in this hypothetical situation is to build the MPI
> application ONCE and then swap run-time libs as newer compilers come
> out.... I am certain that even if one can get away with it with nearby
> run-time versions there is no guarantee of the stability at-infinitum.
> I end up having to spent more time for technically "awkward" requests
> than the reasonable ones. Reminds me when I was a teacher I had to
> spent more time with all the people trying to avoid doing the work
> than with the good students... hmmm :-)
>
According to my understanding, your application (or MPI) built with an
Intel 11.1 compiler should continue working with future Intel 11.1 and
12.x libraries. I don't expect Intel to test or support this
compatibility beyond that.
You will likely want to upgrade your OpenMPI earlier than the time when
Intel compiler changes require a new MPI build.
If the interest is in getting performance benefits of future hardware
simply by installing new dynamic libraries without rebuilding an
application, Intel MKL is the most likely favorable scenario. The MKL
with optimizations for AVX is already in beta test, and should work as
a direct replacement for the MKL in current releases.

-- 
Tim Prince