[mpich-devel] ignoring status cost

[Jeff Hammond]

Thanks.

src/mpi/pt2pt/waitall.c has both code and comments indicating that it
matters.  The ideas for that code came from IBM
(14f8143312e0dfd5eafcaedda8a874f66b912d1a), which presumably means that it
helped on Blue Gene.

It is easy enough to measure message rate with and without an array of
status objects to understand this quantitatively.

Best,

Jeff

On Fri, May 27, 2016 at 6:40 AM, William Gropp <wgropp at illinois.edu> wrote:
>
> This was the motivation, more than avoiding declaring a variable that was
never read in the user’s program.  There was evidence for this from Intel
in the early ‘90s, though I don’t know if anyone has looked into it
recently.
>
> Bill
>
> William Gropp
> Director, Parallel Computing Institute
> Thomas M. Siebel Chair in Computer Science
> Chief Scientist, NCSA
> University of Illinois Urbana-Champaign
>
>
>
>
>
> On May 26, 2016, at 6:30 PM, Jeff Hammond <jeff.science at gmail.com> wrote:
>
> Is it correct to assume that it is cheaper to check for MPI_STATUS_IGNORE
and MPI_STATUSES_IGNORE than to fill in the status object, in the case
where the user does not need the status?
>
> Thanks,
>
> Jeff
>
> --
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
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--
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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