On May 1, 2009, at 8:25 AM, arkady kanevsky wrote:
What if we provide a script which converts all malloc/free
calls into MPI ones and move MPI_INIT before any memory allocation?
Will these application user be willing to do the conversion?
We've been trying to educate MPI application developers for 10
years. :-)
If you think a script will help, go for it. :-)
Sorry; I'm not trying to be snide -- this thread is getting
increasingly frustrating. No, I don't think it will help for a few
reasons:
- MPI's already support malloc/etc. buffers; changing that now would
be a big change -- based on this one network stack.
- MPI's are competitive. If one MPI forces the use of MPI_ALLOC_MEM,
then others will say "you should use my MPI because then you don't
have to change your code to use MPI_ALLOC_MEM." Because we're
ultimately competing for customer's dollars -- MPI's actively try to
make programming/using their product as easy as possible.
- Fortran is always problematic. I haven't thought through the
problems there, but I know of many apps that have huge arrays declared
statically (which the fortran compiler gets from the heap, not the
stack). Forcing them to change to F90-style pointers would never
happen.
- I cited earlier in the thread MPI-based middleware that could do
MPI_ALLOC_MEM (potentially plus a copy) for short messages, but likely
re-uses application buffers directly for large messages because the
copy cost would be too much. Specifically: if MPI is not the top
level middleware in an application -- some other middleware is
fronting the network stack, like a computational library or somesuch
-- they might have to make exactly the same compromises (e.g.,
application buffers are too large, so let's just use those instead of
MPI_ALLOC_MEM+copy).
--
Jeff Squyres
Cisco Systems
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