[mpiwg-rma] same_op_no_op

[Underwood, Keith D]

I'm sure that wasn't Keith making that objection... ;-)

> -----Original Message-----
> From: mpiwg-rma [mailto:mpiwg-rma-bounces at lists.mpi-forum.org] On
> Behalf Of Jeff Hammond
> Sent: Friday, March 14, 2014 12:30 PM
> To: MPI WG Remote Memory Access working group
> Subject: Re: [mpiwg-rma] same_op_no_op
> 
> I'm sure that the WG was too distracted by how many arguments each
> function took to think about semantic issues :-)
> 
> I think not making same_op_no_op_replace the default was just an
> oversight, as you've previously suggested.  I'm sure that Keith has been
> consistent to objecting to atomicity of more than one non-trivial (i.e. not
> NO_OP or REPLACE) op at the same time.  I believe that my previous email
> noting how to use C&S emulation addresses that issue though.
> 
> Jeff
> 
> On Fri, Mar 14, 2014 at 11:25 AM, Brian Barrett <brbarret at open-mpi.org>
> wrote:
> > I agree with Rajeev; concurrent access with different ops wasn't undefined
> in MPI-2.2, it was erroneous.
> >
> > During the Forum meetings on RMA, there was strong opposition to
> relaxing that semantic, which is how we ended up with same_op_no_op.  It
> sucked, but it sucked less than the semantics of MPI-2.2.
> >
> > I'm not opposed to loosening the restrictions (and, in fact, wanted them
> looser during MPI-3), but it would be good to understand why we as a group
> felt that wasn't ok 2 years ago.
> >
> > Brian
> >
> > On Mar 14, 2014, at 6:12 AM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
> >
> >> Where does it say in MPI 2.2 that concurrent accumulates with different
> operations are allowed?
> >>
> >> On pg 365, ln 29-33, it says two concurrent accumulates that use the same
> operation are allowed.
> >>
> >>       • A location in a window must not be accessed as a target of an RMA
> operation once an update to that location has started, until the update
> becomes visible in the public window copy. There is one exception to this
> rule, in the case where the same variable is updated by two concurrent
> accumulates that use the same operation, with the same predefined
> datatype, on the same window.
> >>
> >>
> >> On Mar 14, 2014, at 12:25 AM, "Balaji, Pavan" <balaji at anl.gov> wrote:
> >>
> >>> All,
> >>>
> >>> I’ve written up these thoughts in the below ticket:
> >>>
> >>> https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/416
> >>>
> >>> Comments are welcome on the ticket.
> >>>
> >>> — Pavan
> >>>
> >>> On Mar 13, 2014, at 4:13 PM, Balaji, Pavan <balaji at anl.gov> wrote:
> >>>
> >>>>
> >>>> On Mar 13, 2014, at 4:08 PM, Jeff Hammond <jeff.science at gmail.com>
> wrote:
> >>>>>> It was not disallowed in MPI-2.  I meant that we made a mistake in
> MPI-3 to disallow it since that is not backward compatible.
> >>>>>
> >>>>> You told me two days ago it was at best undefined, which is no
> >>>>> more useful than disallowed:
> >>>>
> >>>> I’m not sure what you are referring to, but that was no my intention.
> Perhaps I misunderstood what you were asking.
> >>>>
> >>>> It think it’s pretty clear that it’s disallowed in MPI-3, not undefined.
> >>>>
> >>>>>> IMO, we should have kept the same semantics as MPI-2, but
> allowed the user to relax it with info arguments.
> >>>>>
> >>>>> Well we broke backwards compatibility but made it almost
> >>>>> impossible for anyone to notice and certainly didn't add an advice
> >>>>> to users so we are clearly all jerks.
> >>>>
> >>>> I like MPI-2’s approach.  The data content is undefined, but not an
> error.
> >>>>
> >>>> — Pavan
> >>>>
> >>>> _______________________________________________
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> >>>> mpiwg-rma at lists.mpi-forum.org
> >>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
> >>>
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> >>
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> >>
> >
> > --
> >  Brian Barrett
> >
> >  There is an art . . . to flying. The knack lies in learning how to
> > throw yourself at the ground and miss.
> >      Douglas Adams, 'The Hitchhikers Guide to the Galaxy'
> >
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> 
> 
> 
> --
> Jeff Hammond
> jeff.science at gmail.com
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