[Mpiwg-large-counts] Large Count - the principles for counts, sizes, and byte and nonbyte displacements

[Jeff Hammond]

Rolf:

Before anybody spends any time analyzing how we handle segmented
addressing, I want you to provide an example of a platform where this is
relevant.  What system can you boot today that needs this and what MPI
libraries have expressed an interest in supporting it?

For anyone who didn't hear, ISO C and C++ have finally committed to
twos-complement integers (
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0907r1.html,
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2218.htm) because modern
programmers should not be limited by hardware designs from the 1960s.  We
should similarly not waste our time on obsolete features like segmentation.

Jeff

On Thu, Oct 24, 2019 at 10:13 AM Rolf Rabenseifner via mpiwg-large-counts <
mpiwg-large-counts at lists.mpi-forum.org> wrote:

> > I think that changes the conversation entirely, right?
>
> Not the first part, the state-of-current-MPI.
>
> It may change something for the future, or a new interface may be needed.
>
> Please, can you describe how MPI_Get_address can work with the
> different variables from different memory segments.
>
> Or whether a completely new function or a set of functions is needed.
>
> If we can still express variables from all memory segments as
> input to MPI_Get_address, there may be still a way to flatten
> the result of some internal address-iquiry into a flattened
> signed integer with the same behavior as MPI_Aint today.
>
> If this is impossible, then new way of thinking and solution
> may be needed.
>
> I really want to see examples for all current stuff as you
> mentioned in your last email.
>
> Best regards
> Rolf
>
> ----- Original Message -----
> > From: "Jeff Squyres" <jsquyres at cisco.com>
> > To: "Rolf Rabenseifner" <rabenseifner at hlrs.de>
> > Cc: "mpiwg-large-counts" <mpiwg-large-counts at lists.mpi-forum.org>
> > Sent: Thursday, October 24, 2019 5:27:31 PM
> > Subject: Re: [Mpiwg-large-counts] Large Count - the principles for
> counts, sizes, and byte and nonbyte displacements
>
> > On Oct 24, 2019, at 11:15 AM, Rolf Rabenseifner
> > <rabenseifner at hlrs.de<mailto:rabenseifner at hlrs.de>> wrote:
> >
> > For me, it looked like that there was some misunderstanding
> > of the concept that absolute and relative addresses
> > and number of bytes that can be stored in MPI_Aint.
> >
> > ...with the caveat that MPI_Aint -- as it is right now -- does not
> support
> > modern segmented memory systems (i.e., where you need more than a small
> number
> > of bits to indicate the segment where the memory lives).
> >
> > I think that changes the conversation entirely, right?
> >
> > --
> > Jeff Squyres
> > jsquyres at cisco.com<mailto:jsquyres at cisco.com>
>
> --
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de .
> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 .
> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 .
> Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner .
> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .
> _______________________________________________
> mpiwg-large-counts mailing list
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>


-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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