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Subject: Re: [OMPI devel] ORTE process name,, nodeid..
From: Tim Prins (tprins_at_[hidden])
Date: 2007-11-19 20:20:43


On Monday 19 November 2007 09:42:21 am Ralph H Castain wrote:
<snip>
> An alternative solution might be to incorporate the modex in the new OMPI
> framework I was about to create anyway. This framework was intended to deal
> with publish/lookup of OMPI data to support a variety of methods.
> Originally, we had intended only to include support there for things
> specifically related to MPI_Publish etc., but there is no reason we
> couldn't generalize it to support the general exchange of process "how to
> connect to me" info and include a modex API in it. I was figuring we would
> need two immediate components in it anyway: an ORTE one for when we have
> full ORTE support in the system, and a CNOS one that would...well, I guess
> just bark and say "you can't do publish/lookup on a Cray". It would be
> simple to add the modex stuff there, and makes some logical sense as well.
I think this approach is fundamentally flawed. Our frameworks are designed to
abstract out something, to allow for multiple implementations. However, doing
this would put two completely different things (the modex and the MPI
pub/sub) together in one framework. While this may be convenient for the
cray, it would be very inconvenient for someone who wanted to do the MPI
pub/sub via a ldap server (as has been discussed). The key here is that MPI
pub/sub is for very small amounts of data, accessed infrequently and in a
non-performance-critical manner, whereas the modex is for rather large
amounts of information (on big jobs) that has to be exchanged efficiently.

Before anyone misunderstands, I am *not* proposing that we add a modex
framework to ompi. Rather, I think this is a case where the RSL could make
things really easy.

The RSL defines a process attribute system. One of the original ideas (later
retracted, but now that I think about it I may re-add it) was to have some
predefined attribute keys, that the runtime would set so we could look up
information about any process.

So in the case of the cray, the rsl_init function would query to get all the
info it wants, and then populate the info into its (local) process attribute
data store.

In other systems each process would set the information in rsl_init and it
would be exchanged in the normal modex method.

Then, the information would be looked up (locally) using the 'get' function on
both platforms.

Simple, eh?

As an alternative to this, I think we could apply these same ideas into a
specialized ORTE system, but it would not be as clean, and would tie our
system closer to ORTE. I am not going to argue whether this is good or bad,
but I am just mentioning it as a consequence.

Tim

>
> If that makes sense, we can implement the latter approach on the branch
> where we are doing the next major ORTE revision - that's where I was going
> to create the new framework anyway.
>
> Ralph
>
> On 11/16/07 10:24 PM, "Shipman, Galen M." <gshipman_at_[hidden]> wrote:
> > I am doing some work on Cray's CNL to support shared memory. To support
> > shared memory I need to know if processes are local or remote. For other
> > systems we simply use the modex in ompi_proc_get_info to get the proc's
> > nodeid. When using CNOS I don't need the modex to get a remote processes
> > nodeid. In fact, I can obtain every processes pid and nodeid (nid/pid)
> > via a single CNOS call.
> >
> > I have explored a couple of ways to populate the proc structures on the
> > CRAY. One involves using #if's to do special things in
> > ompi_proc_get_info. I don't like this. The second method involves adding
> > a CNOS nameserver and modifying the orte_process_name_t to include the
> > orte_nodeid_t so that the nameserver can populate all the info if it can.
> > Prior to this change, the orte_nodeid_t was in ompi_proc_t, which doesn't
> > make any sense to me, it is an orte level concept and it is only
> > accessible in the ompi side. I also don't like adding orte_nodeid_t to
> > orte_process_name_t as it really doesn't have anything to do with the a
> > name.. I think it makes more sense to have an orte_proc_t.. Something
> > like the following structure:
> >
> >
> >
> > struct orte_process_name_t {
> > orte_jobid_t jobid; /**< Job number */
> > orte_vpid_t vpid; /**< Process number */
> > /** "nodeid" on which the proc resides */
> > };
> >
> > Struct orte_proc_t {
> > opal_list_item_t super;
> > orte_process_name_t proc_name;
> > orte_nodeid_t nid;
> > };
> >
> > struct ompi_proc_t {
> > orte_proc_t base;
> > ..... Etc .....
> >
> > };
> >
> >
> > I know there is some talk about removing the process names,,, not sure
> > how that fits in here but this is what makes sense to me given the
> > current architecture. Any thoughts here?
> >
> >
> > - Galen
>
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