[mpiwg-p2p] Next meeting 18th Jan 2016

Jeff Hammond jeff.science at gmail.com
Mon Dec 14 10:19:35 CST 2015

Can someone tell me the best replacement for the following pattern if
freeing active requests is made erroneous?

void send_fire_and_forget_ack(int target, MPI_Comm comm)
  MPI_Request request;
  MPI_Isend(NULL, 0, MPI_BYTE, target, special_tag, comm, &request);

The reason to not use MPI_Send here is it can block on resource exhaustion.

Note that this is a real usage model.  One of my applications send
fire-and-forget acks and it was a performance issue on Blue Gene/Q.
Because we send a payload - it is unclear if this is actually necessary - I
replaced MPI_Send with MPI_Bsend to solve the problem (yes, Bsend really
does help here), but we could instead use Isend+Request_free (which would
be easy since our payload is trivial and could be a global const).

The reason I bring this up even though Bsend works for us is that I would
much rather deprecate Bsend that make freeing active requests erroneous.


On Mon, Dec 14, 2015 at 7:55 AM, Daniel Holmes <dholmes at epcc.ed.ac.uk>

> Hi all,
> The next point-to-point teleconference will be Monday 18th January 2016 at
> 11am Central US via webex.
> I will send out another reminder nearer the time.
> Tentative agenda:
> MPI-4.0, issue #11: add communicator assertions (remember implications for
> tools!)
> MPI-4.0, issue #26: deprecate cancel for send requests
> MPI-4.0, issue TBD: add ARECV/FSEND
> MPI-4.0, issue TBD: deal with minor correction to MPI_WAIT raised by Bill
> and Rajeev (a la Bill's email 29/06/2015)
> * MPI-4.0, issue TBD: deprecate request free for active receive requests
> (arising from Dec 2015 meeting)*
> MPI-4.0, issue TBD: define batch requests (a la Pavan's email of
> 14/12/2015)
> * MPI-Next, issue TBD: disallow request free for active receive requests
> (i.e. upgrade advice to erroneous)*
> MPI-Next, issue #27: disallow cancel for send requests (i.e. upgrade
> advice to erroneous)
> Cheers,
> Dan.
> --
> Dan Holmes
> Applications Consultant in HPC Research
> EPCC, The University of Edinburgh
> James Clerk Maxwell Building
> The Kings Buildings
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> Edinburgh
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> T: +44(0)131 651 3465
> E: dholmes at epcc.ed.ac.uk
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Jeff Hammond
jeff.science at gmail.com
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