[Mpi3-rma] notes from 5pm Tuesday meeting @ July 2012 Forum
jhammond at alcf.anl.gov
Tue Jul 17 22:03:18 CDT 2012
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?
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.
>> -----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
>> 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.
>> 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
>> > _______________________________________________
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>> > 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
>> mpi3-rma mailing list
>> mpi3-rma at lists.mpi-forum.org
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> mpi3-rma at lists.mpi-forum.org
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381
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