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From: Jean-Christophe Hugly (jice_at_[hidden])
Date: 2006-02-08 19:06:28

> you need to specify both the transport and self, such as:
> mpirun -mca btl self,tcp

I found that the reason why I was no-longer able to run without openib
was that I had some openib-specific tunables on the command line. I
expected the params would get ignored, but instead it just sat there.

The other funny thing I found was that on the cmd line I do not need to
specify self; just openib, or tcp will do. But in the param file I must
specify tcp,openib, or self,openib; self,tcp would not work. Oh well, I
do not care for tcp anyway :-).

But should I understand from all this that the "direct" mode will never
actually work ? It seems that if you need at least two transports, then
none of them can be the hardwired unique one, right ? Unless there's a
built-in switch between a built-in self and the built-in other

> For Heroic latencies on IB we would need to use small message RDMA and
> poll each peers dedicated memory region for completion.

Well, I tried to play around with the eager_limit, min_rdma, etc. I did
not see the latency of messages of a given size be lowered by changing
the tresholds to make them rdma'd. Rather the opposite (which was my
initial expectation, actually). May be I just misunderstood the whole
set of tunables. My understanding was that messages under the eager
limit would never be rdma'd by definition, and that the others would or
would not be, depending on the min_rdma_size.

Jean-Christophe Hugly <jice_at_[hidden]>