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Subject: [OMPI users] openmpi credits for eager messages
From: Sacerdoti, Federico (Federico.Sacerdoti_at_[hidden])
Date: 2008-02-01 15:05:27


Hi,

I am readying an openmpi 1.2.5 software stack for use with a
many-thousand core cluster. I have a question about sending small
messages that I hope can be answered on this list.

I was under the impression that if node A wants to send a small MPI
message to node B, it must have a credit to do so. The credit assures A
that B has enough buffer space to accept the message. Credits are
required by the mpi layer regardless of the BTL transport layer used.

I have been told by a Voltaire tech that this is not so, the credits are
used by the infiniband transport layer to reliably send a message, and
is not an openmpi feature.

Thanks,
Federico