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From: Gleb Natapov (glebn_at_[hidden])
Date: 2007-06-13 13:48:36


On Wed, Jun 13, 2007 at 12:35:55PM -0400, Jeff Squyres wrote:
> On Jun 13, 2007, at 12:03 PM, George Bosilca wrote:
>
> >> I think the "hidden" MCA parameters are a different issue; they were
> >> created for a different purpose (users are not supposed to see/set
> >> them). These variable parameters would be intended to be used by the
> >> users, but they would have no way of finding out a) that they exist,
> >> and b) what they are. That's why I think that the MCA parameters may
> >> not be the right mechanism for this kind of information.
> >
> > I see 2 possible solutions:
> >
> > 1. we update our documentation in such a way that it will clearly
> > describe
> > these variable MCA parameters for each BTL that support them.
> >
> > 2. We create fake MCA parameters that will never be used, but they
> > will
> > show up in the ompi_info output so the user will know they exist.
> > For TCP
> > they can be btl_tcp_latency_* and btl_tcp_bandwidth_* ...
>
> Or:
>
> 3. Use a file to convey this information, because it's better suited
> to what we're trying to do (vs. MCA parameters).
>
> Seriously, why is a file a bad thing? The file can list interfaces
> by hostname. For example, if you have a heterogeneous setup, what's
> to say that having btl_tcp_bandwidth_eth0 is not the same across all
> your hosts? That is -- the MCA parameters you're providing are not
> sufficient for a true heterogeneous environment, anyway.
I don't feel strongly one way or the other. The command line approach
was much easier to implement. Is it possible to have one parser for all
BTLs or each one will have to implement different one?a

BTW ompi_info will not parse this file too, so it will not be able to
present correct bandwidth/latency value just like command line solution.
For heterogeneous config file is the only option of cause.

>
> Here's an example file format off the top of my head:
>
> btl-tcp-if.txt:
> host1 eth0=latency,bw eth1=latency,bw
> host2 eth0=latency,bw eth1=latency,bw
>
> Or perhaps you might like the INI-style format:
>
> btl-tcp-if.ini:
> [host1]
> latency_eth0 = x1
> bandwidth_eth0 = y1
> latency_eth1 = x2
> bandwidth_eth1 = y2
>
> ...or pick any other format/variation on the above.
>
> In short: the data you're trying to provide is really (at least) a 2D
> data set (hosts * interfaces). It's just not suitable for MCA
> parameters.
>
> --
> Jeff Squyres
> Cisco Systems
>
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--
			Gleb.