On 6/26/25 21:34, Thomas Koenig wrote:
Am 26.06.25 um 10:15 schrieb Andre Vehreschild:
Hi Thomas,
I have a few questions.
First, I see that your patch series does not use gfortran's descriptors
for accessing coarrays via shared memory, as the original work by
Nicolas did. Can you comment on that?
The ABI for invoking coarray functionality is sufficient for doing the
job.
Modifying the compiler to access coarrays directly, i.e., having
implementation
detail on a certain library in the compiler did not appeal to me.
Furthermore
has the new library in conjunction with the other library available the
potential to get to a stable and maintained ABI. Having another ABI in
the
compiler would have lead to two badly maintained ones (in my opinion). I
therefore decided to just have one ABI and figured that all that is
needed can
be done in a library. This also allows link-time polymorphism. And
last but not
least, there is a major rework on the array descriptor going on and
that would
have had the potential to conflict with my work.
We are very probably not going to get performance out of it that is
comparable with the original design; I would be quite surprised if it
was appreciably better than using shared memory MPI, and in that
case I don't see an advantage of your patch over a better wrapper.
When I learned about the "Koenig" implementation of "native coarrays" in
2018 (as they called it at that time, and I since noticed also Intel
calls it), I wrote a "mock weather forecasting program" using coarrays
to test it against the then working implementation of OpenCoarrays using
MPI calls.
You can find the program here: https://moene.org/~toon/random-weather
[ note that I improved on this program until early in 2021. ]
When I compared the run time of the two implementations with the same
input parameters on a 128 Gbyte RAM Intel machine, the "native"
implementation was around a factor of 5 faster. Of course, the
OpenCoarrays based MPI implementation (using OpenMPI) used shared memory
MPI (which OpenMPI calls "vader" for reasons that escape me).
So I am certainly interested to compare Andre's implementation against
OpenCoarrays.
Kind regards,
--
Toon Moene - e-mail: t...@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
