mpi_test analog

[Jim Edwards]

The memory overhead is on the application end, I need to make a copy of the
iobuffer, because it is potentially reused for each call and if I do
non-blocking calls it needs to persist.

On Mon, Feb 20, 2012 at 2:01 PM, Wei-keng Liao
<wkliao at ece.northwestern.edu>wrote:

> We have a few yet-to-be-published results (using FLASH and a climate
> application) that show significant improvement of using these
> nonblocking (or we should refer them as "aggregating") APIs.
> Below is a scenario that these APIs can be useful. Say, one
> application has many small sized variables defined and they all
> will be written to a file at about the same time, like checkpointing.
> The blocking APIs allow writing/reading one variable at a time,
> so the performance can be poor. The nonblocking APIs aggregate
> multiple requests into a larger one and hence can result in better
> performance.
>
> There is not much overhead for the additional memory management,
> as the APIs do not introduce extra memory copy, nor allocating
> additional buffers. The essence of these APIs are to create a
> new, combined MPI file view for the single collective I/O at
> the end.
>
>
> Wei-keng
>
>
> On Feb 20, 2012, at 2:23 PM, Jim Edwards wrote:
>
> > Hi Wei-keng,
> >
> > That's the answer that I thought I would get, and no I guess there is no
> point in having one.   Is there a demonstrable performance benefit of this
> non-blocking interface that would make it worth taking on the additional
> memory management that it will require?
> >
> > Jim
> >
> > On Mon, Feb 20, 2012 at 1:18 PM, Wei-keng Liao <
> wkliao at ece.northwestern.edu> wrote:
> > Hi, Jim,
> >
> > The "non-blocking" APIs in pnetcdf are not truly asynchronous.
> > They actually defer the I/O requests till ncmpi_wait_all.
> > So, if there is a corresponding test call and it is called
> > in between the post of nonblocking and wait, it will simply
> > return false, indicating not yet complete.
> >
> > Given that, would you still like to see a test API available
> > in pnetcdf? (That will not be too hard to add one.)
> >
> >
> > Wei-keng
> >
> >
> > On Feb 20, 2012, at 1:47 PM, Jim Edwards wrote:
> >
> > > I am working on an async interface using pnetcdf and wondering why
> there is no analog to mpi_test in the API?
> > >
> > > --
> > > Jim Edwards
> > >
> > > CESM Software Engineering Group
> > > National Center for Atmospheric Research
> > > Boulder, CO
> > > 303-497-1842
> > >
> >
> >
> >
> >
> > --
> > Jim Edwards
> >
> >
> >
>
>


-- 

Jim Edwards
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