use of MPI derived types in Flexible API

[Jim Edwards]

Data is contiguous in memory but data on a given task maps to various non
contiguous points in the file.   I can guarantee that the data in memory on
a given mpi task is in monotonically increasing order with respect to
offsets into the file, but not more than that.

On Wed, Sep 24, 2014 at 3:43 PM, Wei-keng Liao <wkliao at eecs.northwestern.edu
> wrote:

> Hi, Jim
>
> Do you mean the local I/O buffer contains a list of non-contiguous data in
> memory?
> Or do you mean "distributed" as data is partitioned across multiple MPI
> processes?
>
> The varm APIs and the "flexible" APIs that take an MPI derived datatype
> argument
> are for users to describe non-contiguous data in the local I/O buffer. The
> imap
> and MPI datatype argument has no effect to the data access in files. So, I
> need
> to know which case you are referring to first.
>
> Thanks for pointing out the error in the user guide. It is fixed.
>
> Wei-keng
>
> On Sep 24, 2014, at 2:30 PM, Jim Edwards wrote:
>
> > I want to write a distributed variable to a file and the way the
> > data is distributed is fairly random with respect to the ordering on the
> file.
> >
> > It seems like I can do several things from each task in order to write
> the data -
> >
> >       • I can specify several blocks of code using start and count and
> make mulitple calls on each task to ncmpi_bput_vara_all
> >       • I can define an MPI derived type and make a single call to
> ncmpi_bput_var_all on each task
> >       • I (think I) can use ncmpi_bput_varm_all and specify an imap
> (btw: the pnetcdf users guide has this interface wrong)
> > Are any of these better from a performance standpoint?
> >
> > Thanks,
> >
> >
> >
> >
> > --
> > Jim Edwards
> >
> > CESM Software Engineer
> > National Center for Atmospheric Research
> > Boulder, CO
>
>


-- 
Jim Edwards

CESM Software Engineer
National Center for Atmospheric Research
Boulder, CO
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