[ofiwg] strided IOVs

[Jeff Hammond]

Both GA/ARMCI and SHMEM utilize regular aka simple strided operations in
RMA.  GA_Acc/ARMCI_AccS/MPI_Accumulate map to fi_atomic, that means those
also need to support strided, assuming RMA does.

I think only simple strided is worth supporting, because it is O(1)
metadata.  General gather/scatter ala iovec is unlikely to optimizable
relative to a higher-level software implementation, so I don't see a good
reason to put it into OFI.

Jeff

On Thu, Oct 29, 2015 at 4:46 AM, Underwood, Keith D <
keith.d.underwood at intel.com> wrote:

> Exactly.  However, we should be careful about what we are adding here.  A
> strided interface is a very specific special case that applies to regular
> problems.  There is a bready of MPI derived datatype capabilities that are
> not covered by a simple stride.  What are the objectives for covering
> datatypes?  Is the IOVEC interface the right place to glue in the first
> handling of a special case of datatypes?
>
> > -----Original Message-----
> > From: ofiwg-bounces at lists.openfabrics.org [mailto:ofiwg-
> > bounces at lists.openfabrics.org] On Behalf Of Hefty, Sean
> > Sent: Wednesday, October 28, 2015 3:14 PM
> > To: Hefty, Sean <sean.hefty at intel.com>; Howard Pritchard
> > <hppritcha at gmail.com>
> > Cc: ofiwg at lists.openfabrics.org
> > Subject: Re: [ofiwg] strided IOVs
> >
> > > I need more context to understand how writing X bytes every N bytes
> > > into a one-time use receive buffer is useful.
> >
> > FWIW, someone sent me this link:
> >
> > http://people.csail.mit.edu/fred/ghost_cell.pdf
> >
> > as an example.
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-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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