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From: Tim Prins (tprins_at_[hidden])
Date: 2007-08-21 14:28:00


Yeah, ABI is something that has been on many people's "it would be nice
to have this someday" list, but I agree with Terry in that if this is
something we want, MPI is the place to start.

I assume that the RSL will have the same ABI problems as every other
framework.

Tim

Terry D. Dontje wrote:
> Matthias Mueller wrote:
>
>> Tim, all,
>>
>> I believe that such an effort also would be an opportunity to come up
>> with a strategy regarding upwards and downwards compatibility (will a
>> binary compiled with one version work within the runtime of a different
>> version?). IMHO this is what is needed by ISV when they ship binaries,
>> it is alo needed by any user who doesn't want to recompile after any
>> (minor) upgrade by the sysadmins.
>>
>>
> This seems like a lot wider topic than just the ORTE. I really think that
> if the community was going to attack the ABI compatibiltiy we really
> should start at the MPI interface area.
>
> --td
>
>> AFAIK Open MPI does not have a (strong or advertised) commitment
>> regarding compatibility. It would be nice to have such a commitment and
>> also proper error messages when someone tries to run a binary in an
>> environment that is not compatible.
>>
>> Best regards,
>> Matthias
>>
>> On Thu, 2007-08-16 at 21:47 -0400, Tim Prins wrote:
>>
>>
>>> WHAT: Solicitation of feedback on the possibility of adding a runtime
>>> services layer to Open MPI to abstract out the runtime.
>>>
>>> WHY: To solidify the interface between OMPI and the runtime environment,
>>> and to allow the use of different runtime systems, including different
>>> versions of ORTE.
>>>
>>> WHERE: Addition of a new framework to OMPI, and changes to many of the
>>> files in OMPI to funnel all runtime request through this framework. Few
>>> changes should be required in OPAL and ORTE.
>>>
>>> WHEN: Development has started in tmp/rsl, but is still in its infancy. We hope
>>> to have a working system in the next month.
>>>
>>> TIMEOUT: 8/29/07
>>>
>>> ------
>>> Short version:
>>>
>>> I am working on creating an interface between OMPI and the runtime system.
>>> This would make a RSL framework in OMPI which all runtime services would be
>>> accessed from. Attached is a graphic depicting this.
>>>
>>> This change would be invasive to the OMPI layer. Few (if any) changes
>>> will be required of the ORTE and OPAL layers.
>>>
>>> At this point I am soliciting feedback as to whether people are
>>> supportive or not of this change both in general and for v1.3.
>>>
>>>
>>> Long version:
>>>
>>> The current model used in Open MPI assumes that one runtime system is
>>> the best for all environments. However, in many environments it may be
>>> beneficial to have specialized runtime systems. With our current system this
>>> is not easy to do.
>>>
>>> With this in mind, the idea of creating a 'runtime services layer' was
>>> hatched. This would take the form of a framework within OMPI, through which
>>> all runtime functionality would be accessed. This would allow new or
>>> different runtime systems to be used with Open MPI. Additionally, with such a
>>> system it would be possible to have multiple versions of open rte coexisting,
>>> which may facilitate development and testing. Finally, this would solidify the
>>> interface between OMPI and the runtime system, as well as provide
>>> documentation and side effects of each interface function.
>>>
>>> However, such a change would be fairly invasive to the OMPI layer, and
>>> needs a buy-in from everyone for it to be possible.
>>>
>>> Here is a summary of the changes required for the RSL (at least how it is
>>> currently envisioned):
>>>
>>> 1. Add a framework to ompi for the rsl, and a component to support orte.
>>> 2. Change ompi so that it uses the new interface. This involves:
>>> a. Moving runtime specific code into the orte rsl component.
>>> b. Changing the process names in ompi to an opaque object.
>>> c. change all references to orte in ompi to be to the rsl.
>>> 3. Change the configuration code so that open-rte is only linked where needed.
>>>
>>> Of course, all this would happen on a tmp branch.
>>>
>>> The design of the rsl is not solidified. I have been playing in a tmp branch
>>> (located at https://svn.open-mpi.org/svn/ompi/tmp/rsl) which everyone is
>>> welcome to look at and comment on, but be advised that things here are
>>> subject to change (I don't think it even compiles right now). There are
>>> some fairly large open questions on this, including:
>>>
>>> 1. How to handle mpirun (that is, when a user types 'mpirun', do they
>>> always get ORTE, or do they sometimes get a system specific runtime). Most
>>> likely mpirun will always use ORTE, and alternative launching programs would
>>> be used for other runtimes.
>>> 2. Whether there will be any performance implications. My guess is not,
>>> but am not quite sure of this yet.
>>>
>>> Again, I am interested in people's comments on whether they think adding
>>> such abstraction is good or not, and whether it is reasonable to do such a
>>> thing for v1.3.
>>>
>>> Thanks,
>>>
>>> Tim Prins
>>> _______________________________________________
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>>> devel-core_at_[hidden]
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>>>
>>>
>
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