[mpiwg-rma] RMA Errata

[William Gropp]

I believe that this is not only a pragmatic approach, but the correct one.  You should be able to use the C11 atomic  memory features to have a portable shared memory code (once we have full C11 compilers).

Bill

On Jan 28, 2015, at 11:22 PM, Jeff Hammond <jeff.science at gmail.com> wrote:

> Thanks.  I understand that this isn't an easy issue.  We are trying to
> use MPI-3 shared memory windows internally with PSCW-like
> synchronization and I am inclined to just give up and use x86
> intrinsics to do what I know is sufficient for our processors and
> compilers, just to make it easy (and fast).
> 
> Jeff
> 
> On Wed, Jan 28, 2015 at 1:43 PM, William Gropp <wgropp at illinois.edu> wrote:
>> That’s a harder topic and I wanted to think more about it.  Here are the two
>> issues with which I am most concerned:
>> 
>> 1) We are defining the interaction of MPI with stuff that happens outside of
>> MPI, in the programming language.  Yes, we always sort of did, but this is
>> in an area where many skilled people have made mistakes, and the likelyhood
>> of an error is much higher.  The lack of precision in these discussions
>> reinforces my concern.
>> 
>> 2) We are not considering the potential overhead that requiring other than a
>> small set of RMA synchronization routines to guarantee some shared memory
>> synchronization.  The sense that I get is that the Forum is unconcerned
>> about this, which I think is a serious mistake, and one for which I have yet
>> to see a compelling use case.
>> 
>> Bill
>> 
>> On Jan 28, 2015, at 7:46 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
>> 
>> Fine, but it would be helpful if you would respond to my comments
>> about allowing point-to-point _synchronization_ on shared memory using
>> PSCW, since those were the more germane ones anyways.
>> 
>> 
>> 
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> 
> 
> 
> -- 
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
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