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Subject: Re: [OMPI devel] RFC: Move of ompi_bitmap_t
From: Brian Barrett (brbarret_at_[hidden])
Date: 2009-02-01 14:20:40


While I would love to be involved in this change, as I believe it's
critical it get done right and have some reservations based on the
work we did while a bunch of us were still at LANL, I just don't have
time for yet another weekly telecon (particularly since 2:00 MST is
the same as an existing weekly telecon).

I still think my objections stand, however. A weekly telecon to
discuss the issues is no replacement for a detailed explanation of how
things are going to work, as well as some proof of concept code. We
should hold this change up to the same standard we hold all major
changes to -- which means a working temp branch with negligible
performance impact.

Brian

On Feb 1, 2009, at 12:14 PM, Graham, Richard L. wrote:

> Brian,
> Just fyi, there is a weekly call - thursdays at 4 est where we have
> been discussyng these issues.
> Let's touch base at the forum.
>
> Rich
>
> ----- Original Message -----
> From: devel-bounces_at_[hidden] <devel-bounces_at_[hidden]>
> To: Open MPI Developers <devel_at_[hidden]>
> Sent: Sun Feb 01 10:36:33 2009
> Subject: Re: [OMPI devel] RFC: Move of ompi_bitmap_t
>
> In that case, I remove my objection to this particular RFC. It
> remains for all other RFCs related to moving any of the BTL move code
> to the trunk before the critical issues with the BTL move have been
> sorted out in a temporary branch. This includes renaming functions
> and such. Perhaps we should have a discussion about those issues
> during the Forum in a couple weeks?
>
> Brian
>
> On Feb 1, 2009, at 5:37 AM, Jeff Squyres wrote:
>
>> I just looked through both opal_bitmap_t and ompi_bitmap_t and I
>> think that the only real difference is that in the ompi version, we
>> check (in various places) that the size of the bitmap never grows
>> beyond OMPI_FORTRAN_HANDLE_MAX; the opal version doesn't do these
>> kind of size checks.
>>
>> I think it would be fairly straightforward to:
>>
>> - add generic checks into the opal version, perhaps by adding a new
>> API call (opal_bitmap_set_max_size())
>> - if the max size has been set, then ensure that the bitmap never
>> grows beyond that size, otherwise let it have the same behavior as
>> today (grow without bound -- assumedly until malloc() fails)
>>
>> It'll take a little care to ensure to merge the functionality
>> correctly, but it is possible. Once that is done, you can:
>>
>> - remove the ompi_bitmap_t class
>> - s/ompi_bitmap/opal_bitmap/g in the OMPI layer
>> - add new calls to opal_bitmap_set_max_size(&bitmap,
>> OMPI_FORTRAN_HANDLE_MAX) in the OMPI layer (should only be in a few
>> places -- probably one for each MPI handle type...? It's been so
>> long since I've looked at that code that I don't remember offhand)
>>
>> I'd generally be in favor of this because, although this is not a
>> lot of repeated code, it *is* repeated code -- so cleaning it up and
>> consolidating the non-Fortran stuff down in opal is not a Bad Thing.
>>
>>
>> On Jan 30, 2009, at 4:59 PM, Ralph Castain wrote:
>>
>>> The history is simple. Originally, there was one bitmap_t in orte
>>> that was also used in ompi. Then the folks working on Fortran found
>>> that they had to put a limit in the bitmap code to avoid getting
>>> values outside of Fortran's range. However, this introduced a
>>> problem - if we had the limit in the orte version, then we limited
>>> ourselves unnecessarily, and introduced some abstraction questions
>>> since orte knows nothing about Fortran.
>>>
>>> So two were created. Then the orte_bitmap_t was blown away at a
>>> later time when we removed the GPR as George felt it wasn't
>>> necessary (which was true). It was later reborn when we needed it
>>> in the routed system, but this time it was done in opal as others
>>> indicated a potential more general use for that capability.
>>>
>>> The problem with uniting the two is that you either have to
>>> introduce Fortran-based limits into opal (which messes up the non-
>>> ompi uses), or deal with the Fortran limits in some other fashion.
>>> Neither is particularly pleasant, though it could be done.
>>>
>>> I think it primarily is a question for the Fortran folks to address
>>> - can they deal with Fortran limits in some other manner without
>>> making the code unmanageable and/or taking a performance hit?
>>>
>>> Ralph
>>>
>>>
>>> On Jan 30, 2009, at 2:40 PM, Richard Graham wrote:
>>>
>>>> This should really be viewed as a code maintenance RFC. The
>>>> reason this
>>>> came up in the first place is because we are investigating the btl
>>>> move, but
>>>> these are really two very distinct issues. There are two bits of
>>>> code that
>>>> have virtually the same functionality - they do have the same
>>>> interface I am
>>>> told. The question is, is there a good reason to keep two
>>>> different
>>>> versions in the repository ? Not knowing the history of why a
>>>> second
>>>> version was created this is an inquiry. Is there some performance
>>>> advantage, or some other advantage to having these two versions ?
>>>>
>>>> Rich
>>>>
>>>>
>>>> On 1/30/09 3:23 PM, "Terry D. Dontje" <Terry.Dontje_at_[hidden]> wrote:
>>>>
>>>>> I second Brian's concern. So unless this is just an announcement
>>>>> that
>>>>> this is being done on a tmp branch only until everything is in
>>>>> order I
>>>>> think we need further discussions.
>>>>>
>>>>> --td
>>>>>
>>>>> Brian Barrett wrote:
>>>>>> So once again, I bring up my objection of this entire line of
>>>>>> moving
>>>>>> until such time as the entire process is properly mapped out. I
>>>>>> believe it's premature to being moving around code in
>>>>>> preparation for
>>>>>> a move that hasn't been proven viable yet. Until there is
>>>>>> concrete
>>>>>> evidence that such a move is possible, won't degrade application
>>>>>> performance, and does not make the code totally unmaintainable, I
>>>>>> believe that any related code changes should not be brought into
>>>>>> the
>>>>>> trunk.
>>>>>>
>>>>>> Brian
>>>>>>
>>>>>>
>>>>>> On Jan 30, 2009, at 12:30 PM, Rainer Keller wrote:
>>>>>>
>>>>>>> On behalf of Laurent Broto
>>>>>>>
>>>>>>> RFC: Move of ompi_bitmap_t
>>>>>>>
>>>>>>> WHAT: Move ompi_bitmap_t into opal or onet-layer
>>>>>>>
>>>>>>> WHY: Remove dependency on ompi-layer.
>>>>>>>
>>>>>>> WHERE: ompi/class
>>>>>>>
>>>>>>> WHEN: Open MPI-1.4
>>>>>>>
>>>>>>> TIMEOUT: February 3, 2009.
>>>>>>>
>>>>>>> -------------------------------------
>>>>>>> Details:
>>>>>>> WHY:
>>>>>>> The ompi_bitmap_t is being used in various places within
>>>>>>> opal/orte/ompi. With
>>>>>>> the proposed splitting of BTLs into a separate library, we are
>>>>>>> currently
>>>>>>> investigating several of the differences between ompi/class/*
>>>>>>> and
>>>>>>> opal/class/*
>>>>>>>
>>>>>>> One of the items is the ompi_bitmap_t which is quite similar to
>>>>>>> the
>>>>>>> opal_bitmap_t.
>>>>>>> The question is, whether we can remove favoring a solution just
>>>>>>> in opal.
>>>>>>>
>>>>>>> WHAT:
>>>>>>> The data structures in the opal-version are the same,
>>>>>>> so is the interface,
>>>>>>> the implementation is *almost* the same....
>>>>>>>
>>>>>>> The difference is the Fortran handles ;-]!
>>>>>>>
>>>>>>> Maybe we're missing something but could we have a discussion,
>>>>>>> on why
>>>>>>> Fortran
>>>>>>> sizes are playing a role here, and if this is a hard
>>>>>>> requirement, how
>>>>>>> we could
>>>>>>> settle that into that current interface (possibly without a
>>>>>>> notion of
>>>>>>> Fortran,
>>>>>>> but rather, set some upper limit that the bitmap may grow to?)
>>>>>>>
>>>>>>> With best regards,
>>>>>>> Laurent and Rainer
>>>>>>> --
>>>>>>> ------------------------------------------------------------------------
>>>>>>> Rainer Keller, PhD Tel: (865) 241-6293
>>>>>>> Oak Ridge National Lab Fax: (865) 241-4811
>>>>>>> PO Box 2008 MS 6164 Email: keller_at_[hidden]
>>>>>>> Oak Ridge, TN 37831-2008 AIM/Skype: rusraink
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> devel mailing list
>>>>>>> devel_at_[hidden]
>>>>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>>>>>>
>>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>
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>>>
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>>
>>
>> --
>> Jeff Squyres
>> Cisco Systems
>>
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-- 
   Brian Barrett
   Open MPI developer
   http://www.open-mpi.org/