[Mpi3-rma] notes from 5pm Tuesday meeting @ July 2012 Forum

[Jeff Hammond]

And note that I strongly agree with the existing consensus "to stick
with the existing text which permits only 'C integer, Fortran integer,
Logical, Multi-language types, or Byte'."

Floating-point atomics should be a separate ticket since they are new
semantics that I don't believe that anyone has thought about properly
yet.  Someone should think hard about what they mean and try to get
this feature in MPI-Next.

Jeff

On Tue, Jul 17, 2012 at 10:03 PM, Jeff Hammond <jhammond at alcf.anl.gov> wrote:
> What do you mean by "arbitrary atomics"?  Are you proposing to do
> something evil with bitwise comparison on floating-point numbers to
> realize something other than the obvious meaning of CAS on a float
> type?  If so, just say it, then do it the right way.
>
> We should consider how users will interpret CAS on doubles, for
> example, and not what some low-level network person can dream up to do
> with this operation.
>
> What architecture implements remote CAS on floating-point types in
> hardware right now?  Who is proposing it?  I invoke the standard (and
> a bit worn out) argument about implementing MPI-3 entirely in hardware
> and say that unless someone knows how to do CAS for doubles, it cannot
> be in the standard.
>
> And to be perfectly honest, I have utterly no idea what you really
> mean right now so it would be very helpful if you could be very
> explicit about what you mean by CAS on floating point types.  What
> measure are you using for comparison?  Does this have any reason
> meaning in the context of floating point arithmetic?
>
> Jeff
>
> On Tue, Jul 17, 2012 at 9:40 PM, Underwood, Keith D
> <keith.d.underwood at intel.com> wrote:
>> Floating-point CAS is valid as a way to implement "if this hasn't changed, put the results of this operation in place".  It gives you a (moderately expensive, not very fair) way to build a form of arbitrary atomics.
>>
>> Keith
>>
>>> -----Original Message-----
>>> From: mpi3-rma-bounces at lists.mpi-forum.org [mailto:mpi3-rma-
>>> bounces at lists.mpi-forum.org] On Behalf Of Jeff Hammond
>>> Sent: Tuesday, July 17, 2012 7:26 PM
>>> To: MPI 3.0 Remote Memory Access working group
>>> Subject: Re: [Mpi3-rma] notes from 5pm Tuesday meeting @ July 2012
>>> Forum
>>>
>>> I don't know that floating-point compare is well-defined.  You really have ask
>>> "if abs(x-y)<tolerance" and not "if x==y".
>>>
>>> I think only fixed-point types should be valid for CAS.
>>>
>>> Jeff
>>>
>>> On Tue, Jul 17, 2012 at 6:14 PM, Dave Goodell <goodell at mcs.anl.gov> wrote:
>>> > Discussed the complex types in COMPARE_AND_SWAP issue.  "Fortran
>>> Integer" category is permitted, but "Complex" category is not, primarily
>>> because of width.  Since "Fortran Integer" contains wide types, shouldn't we
>>> just permit "Complex" and "Floating point" as well?  Consensus was to stick
>>> with the existing text which permits only "C integer, Fortran integer, Logical,
>>> Multi-language types, or Byte".
>>> >
>>> > Group review (esp. Jim & Sreeram):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/187
>>> >
>>> > incorporate Jim suggested change (Torsten):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/271
>>> >
>>> > we think we are unaffected, but need a second check (Jim):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/278
>>> >
>>> > Double-check that C++ is not referenced in the RMA chapter (Pavan):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/281
>>> >
>>> > Needs review (Dave):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/300
>>> >
>>> > Think unaffected, but slim chance of Rput/Rget being affected (Pavan):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/317
>>> >
>>> > Need to check implementation of various (4?) "flush is non-local"
>>> > changes (Dave):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/270
>>> >
>>> > Need to check disp_unit change (Jim & Sreeram):
>>> > https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/284
>>> >
>>> > After the above items have all been dealt with, all chapter committee
>>> members should re-read the whole chapter in the *clean* document (the
>>> one _without_ the changebars and colored text) to look for obvious typos
>>> and inconsistencies.
>>> >
>>> > -Dave
>>> >
>>> >
>>> > _______________________________________________
>>> > mpi3-rma mailing list
>>> > mpi3-rma at lists.mpi-forum.org
>>> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>>
>>>
>>>
>>> --
>>> Jeff Hammond
>>> Argonne Leadership Computing Facility
>>> University of Chicago Computation Institute jhammond at alcf.anl.gov / (630)
>>> 252-5381 http://www.linkedin.com/in/jeffhammond
>>> https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond
>>>
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>>> mpi3-rma at lists.mpi-forum.org
>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>
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>
>
>
> --
> Jeff Hammond
> Argonne Leadership Computing Facility
> University of Chicago Computation Institute
> jhammond at alcf.anl.gov / (630) 252-5381
> http://www.linkedin.com/in/jeffhammond
> https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond



-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
http://www.linkedin.com/in/jeffhammond
https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond