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Subject: Re: [OMPI devel] Simple program (103 lines) makes Open-1.4.3 hang
From: Eugene Loh (eugene.loh_at_[hidden])
Date: 2010-11-23 17:45:10

Sébastien Boisvert wrote:
Le mardi 23 novembre 2010 à 16:07 -0500, Eugene Loh a écrit :
Sébastien Boisvert wrote:
Case 1: 30 MPI ranks, message size is 4096 bytes

File: mpirun-np-30-Program-4096.txt
Outcome: It hangs -- I killed the poor thing after 30 seconds or so.
4096 is rendezvous.  For eager, try 4000 or lower.
According to ompi_info, the threshold is 4096, not 4000, right ?
"btl_sm_eager_limit: Below this size, messages are sent "eagerly" --
that is, a sender attempts to write its entire message to shared buffers
without waiting for a receiver to be ready. Above this size, a sender
will only write the first part of a message, then wait for the receiver
to acknowledge its ready before continuing. Eager sends can improve
performance by decoupling senders from receivers."


It should say "Below this size or equal to this size" instead of "Below
this size" as ompi_info says. ;)
Well, I guess it should say:

If message data plus header information fits within this limit, the message is sent "eagerly"...

I guess I'll fix it.  (I suspect I wrote it in the first place.  Sigh.)