Terry Dontje wrote:
Richard Graham wrote:
Terry,
Is there any way you can quantify the cost ? This seems
reasonable, but
would be nice to get an idea what the performance cost is (and not
within a
tight loop where everything stays in cache).
Rich
Ok, I guess that would eliminate any of the simple perf tests like
IMB, netperf, and such. So do you have something else in mind, maybe
HPCC?
Rich,
I retract the above. HPCC and IMB probably doesn't use the predefines
that much. One might be able to just do a lot of MPI_Comm_rank calls
but then you run into the caching problems you mention above. Though I
wonder if we do enough runs and compare the first call if that might be
enough.
--td
--td
On 12/16/08 10:41 AM, "Terry D. Dontje" <terry.don...@sun.com> wrote:
WHAT: To make predefined handles extern to pointers instead of an
address of an extern to a structure.
WHY: To make OMPI more backwards compatible in regards to changes to
structures that define predefined handles.
WHERE: In the trunk. ompi/include/mpi.h.in and places in ompi that
directly use the predefined handles.
WHEN: 01/24/2009
TIMEOUT: 01/10/2009
____________________
The point of this change is to improve the odds that an MPI application
does not have to recompile when changes are made to the OMPI library.
In this case specifically the predefined handles that use the
structures
for communicators, groups, ops, datatypes, error handlers, win, file,
and info.
An example of the changes for the communicator predefined handles
can be
found in the hg tmp workspace at
ssh://www.open-mpi.org/~tdd/hg/predefcompat.
Note, the one downfall that Jeff and I could think of by doing this is
you potentially add one level of indirection but I believe that will be
a small overhead and if you use one of the predefined handles
repetitively (like in a loop) that the address will probably be stored
in a register once and no additional over should be seen due to this
change.
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