[Mpi3-subsetting] MPI subsetting: charting the way forward atatelecon next week?

[Martin Schulz]

At 10:12 AM 6/20/2008, Richard Treumann wrote:

>Of course -
>
>An assertion is a statement that the application does not require 
>some MPI standard feature or semantic guarantee. It is not a 
>directive to the MPI implementation. The implementation is free to 
>provide that feature or guarantee even if the application says it is 
>not needed.
>
>The story is a bit different for a helper library because the 
>library is logically a more or less opaque part of the application. 
>If the caller of MPI_INIT_ASSERTED says the application does not 
>require something and then uses a library that does require that 
>feature or guarantee - the library must raise an error or adjust its 
>behavior to live within the assertion.

While I understand the intention, am a bit worried about the
implications. Imagine a long running application that loads
a new physics module after hours of computation and this new
module requires different assertions. If the only option it
has is to fail, a lot of progress in the main application will
get lost. The only alternative is for the application to never
state any assertion since it does not know which modules it
will load (often depends on the input deck) - and then the
whole exercise will be pointless anyway.

Also, tools often need very specific MPI features and can't live
with many assertions (just taking from Rich's examples in the
other emails: there is often a need to use wildcards or complex
datatypes even if the application doesn't use it). Not being
able to change this would basically eliminate the ability to
use certain tools on certain applications (I realize that tools
that run from the beginning can intercept MPI_Init and turn
assertions off, but tools that attach can't).

Hence, I think we need some way to change assertions at runtime
(at very specific points only and as global operations) despite
the extra complexity it will introduce.

Martin

>Dick Treumann - MPI Team/TCEM
>IBM Systems & Technology Group
>Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
>Tele (845) 433-7846 Fax (845) 433-8363
>
>
>mpi3-subsetting-bounces_at_[hidden] wrote on 06/20/2008 12:58:03 PM:
>
> > Hi,
> >
> > Ignoring an assertion should be perfectly legal.
> >
> > Best regards.
> >
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>mpi3-subsetting mailing list
>mpi3-subsetting_at_[hidden]
>http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-subsetting

_______________________________________________________________________
Martin Schulz, schulzm_at_[hidden], http://people.llnl.gov/schulz6
CASC @ Lawrence Livermore National Laboratory, Livermore, USA  





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