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From: Troy Telford (ttelford_at_[hidden])
Date: 2005-11-21 10:34:03


On Mon, 21 Nov 2005 06:00:05 -0700, Jeff Squyres <jsquyres_at_[hidden]>
wrote:

> Although George fixed the MX-abort error, let me clarify the rationale
> here...
>
> You are correct that at run-time, OMPI tries to load an run every
> component that it finds. So if you have BTL components build for all
> interconnects, OMPI will query each of them at run-time and try to use
> them.
>
> But right now, we do not have a way to show exactly which interconnects
> and which networks are actually being used. Although this is a planned
> feature, for 1.0 we compromised and decided that if any of the
> low-latency/high-speed network components decided that they could not
> be used, they would print out a warning message. This should cover
> 95+% of misconfiguration cases (e.g., the user meant to be using IB,
> but something went wrong and OMPI failed over to TCP).

It's certainly not a bad thing IMHO, either. It's pretty obvious there's
*something* wrong when you can only see 20 MB/sec over Infiniband. (It's
certainly easier to diagnose exactly what /something/ when the cluster's
Ethernet switch is a 10/100, not Gig-E.)

> These warnings will likely be removed (or, more specifically, only
> displayed if requested) once we include the feature to display which
> BTL components/networks are being used at run-time.

While only really useful for testing, it would be neat to be able to say
'try to use every component execept this one.' For instance, should I
feel the need to scratch the itch of using IP-over-IB or TCP over Myrinet
-- in my case, this would mainly be because of my cluster's 10/100 switch,
and I'd like to test/tune either OMPI's TCP performance, or IPoIB/TCPoMyri
driver performance. In such a case, I could say 'ignore mvapi; yes RDMA
is good, sure it's a silly thing do do -- now bow to my will ye minions,
and despair.'

Naturally, I could do this by simply removing the openib, mvapi, gm,
and/or mx components; but that would require typing more characters than
'--ignore_mca btl gm'.