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Subject: [OMPI users] debugging performance regressions between versions
From: Dave Love (d.love_at_[hidden])
Date: 2013-10-18 12:17:36


I've been testing an application that turns out to be ~30% slower with
OMPI 1.6.5 than (the Red Hat packaged version of) 1.5.4, with the same
mca-params and the same binary, just flipping the runtime. It's running
over openib, and the profile it prints says that alltoall is a factor of
four slower in 1.6.5. (I haven't tried to profile it externally, but
I've no reason to doubt what it says.)

How should I go about finding out why and -- I hope -- fixing it?

A possibly relevant side question: Is there a way of dumping all the
MCA parameters in effect? ompi_info --all doesn't show collective
algorithms, for instance, though I thought I'd got those out of it at
one time.