[mpich-devel] code path for non-blocking operations that are deferred until synchronization

[Zhou, Hui]

Hi Jeff,

The nonblocking cases can also do the same support by copying to and from contiguous buffers if we stick the temporary buffer pointer in the request object and free it upon completion. But if you are looking at this from the Fortran binding layer, which does not have access to MPICH internals, then it is difficult to do. The straight-forward solution would be ask MPICH to add an extension, so the user can stick the buffer pointer somewhere, for example, the status object.

I wonder if there is a code path in MPICH associated with nonblocking communication that is deferred until the request is synchronized.  For example, is there code that merely copies all the arguments passed to the call into some object and then processes the whole operation when the request is synchronized?
I am not exactly sure what do you mean here, but the persistent request most resembles your idea of merely hold all the arguments and only process it at start time. But again, if you are not allowed to access MPICH internals, then that is out-of-reach.

--
Hui

________________________________
From: Jeff Hammond via devel <devel at mpich.org>
Sent: Thursday, January 5, 2023 4:50 AM
To: MPICH <devel at mpich.org>
Cc: Jeff Hammond <jeff.science at gmail.com>
Subject: [mpich-devel] code path for non-blocking operations that are deferred until synchronization

This is related to https://github.com/mpi-forum/mpi-issues/issues/663 but there are other scenarios where nonblocking communication with non-contiguous Fortran subarrays is extremely difficult to implement.  The blocking cases are easy to support by copying to and from contiguous buffers.

I wonder if there is a code path in MPICH associated with nonblocking communication that is deferred until the request is synchronized.  For example, is there code that merely copies all the arguments passed to the call into some object and then processes the whole operation when the request is synchronized?

Critically for my case, the Fortran arguments would need to be copied, meaning the CFI_cdesc_t pointer not just the associated base_addr, which I doubt is there based on what I've read so far.

Thanks,

Jeff

--
Jeff Hammond
jeff.science at gmail.com<mailto:jeff.science at gmail.com>
http://jeffhammond.github.io/
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