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Subject: Re: [OMPI devel] [PATCH] openib: clean-up connect to allow for new cm's
From: Jon Mason (jon_at_[hidden])
Date: 2007-12-12 15:21:57


On Wed, Dec 12, 2007 at 01:35:33PM -0500, Jeff Squyres wrote:
> I agree with Gleb's idea. More below.
>
> On Dec 12, 2007, at 12:24 PM, Jon Mason wrote:
>
> > Ok, glad I got this conversation started :)
> >
> > So, we need a slight redesign to determine the cm method (unless
> > forced
> > via commandline arg). This can be determined by calling all the
> > individual open routines, and having them return a priority based on
> > their ability to function. For example, the xoob open function will
> > check the mca_btl_openib_component.num_xrc_qps for a non-zero value
> > and
> > return the priority based on that.
> >
> > Of course, if forced then it will only call that specific open
> > function
> > and throw any relevant errors as necessary.
>
>
> Close, but I'd do it slightly differently:
>
> - open() is *only* used for creating MCA params. It's a bad name, but
> it's unfortunately the precedent throughout the rest of the OMPI code
> base. :-\ (it has roots in the ompi_info command -- ompi_info has to
> be able to get a full list of all MCA params regardless of what
> hardware is available on the current system)
>
> - during the openib component startup, we should add a query()
> function that does what you describe. I.e., we query() each endpoint
> and it either returns a valid priority or "I don't want to be used
> with this endpoint."
>
> - there should be a priority MCA param for every CPC. Perhaps the CPC
> base can handle this...? I'm not sure; it may need to be down in each
> CPC.
>
> - the list of CPCs that want to run with each endpoint are ordered by
> priority (ties will be arbitrarily, but deterministically, broken --
> alphabetical?) and sent around in the modex.
>
> - when a new connection comes up, the intersection of the CPC lists
> for the near and far endpoints is computed and the highest priority
> CPC is used to make the connection. Since everyone has the same data,
> both sides will make the same decision.
>
> - CPC init may have to change a bit -- more than one CPC may be used
> for a given endpoint because both the local module and the remote
> module are involved in making the decision of which CPC is used.
>
> After this first cut is done, we should probably also add
> btl_openib_cpc_include and btl_openib_cpc_exclude as I described in a
> prior mail (just like *_if_include and *_if_exclude in several BTLs)
> to include/exclude sets of CPCs at run-time.
>
> > If this sounds sane, then let me know and I'll start coding it up.
>
>
> This has actually been on my to-do list for too long; if you have the
> cycles to do this now, it would be great...

Since I need to have it done before I can do my rdma_cm bits, I'll add
this to my queue and get started immediately.

>
> I'll make you a bargain: if you do the stuff above, I'll add in the
> configure/build mojo for selectively compiling the XOOB CPC or not
> (depending on whether the underlying system has XRC library support or
> not). Cool?
>
> Let's go off on a /tmp-public branch for this so we don't hose the
> trunk... I just made /tmp-public/openib-cpc.
>
> --
> Jeff Squyres
> Cisco Systems
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