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From: Tim Prins (tprins_at_[hidden])
Date: 2007-08-16 21:47:09

WHAT: Solicitation of feedback on the possibility of adding a runtime
services layer to Open MPI to abstract out the runtime.

WHY: To solidify the interface between OMPI and the runtime environment,
and to allow the use of different runtime systems, including different
versions of ORTE.

WHERE: Addition of a new framework to OMPI, and changes to many of the
files in OMPI to funnel all runtime request through this framework. Few
changes should be required in OPAL and ORTE.

WHEN: Development has started in tmp/rsl, but is still in its infancy. We hope
to have a working system in the next month.

TIMEOUT: 8/29/07

Short version:

I am working on creating an interface between OMPI and the runtime system.
This would make a RSL framework in OMPI which all runtime services would be
accessed from. Attached is a graphic depicting this.

This change would be invasive to the OMPI layer. Few (if any) changes
will be required of the ORTE and OPAL layers.

At this point I am soliciting feedback as to whether people are
supportive or not of this change both in general and for v1.3.

Long version:

The current model used in Open MPI assumes that one runtime system is
the best for all environments. However, in many environments it may be
beneficial to have specialized runtime systems. With our current system this
is not easy to do.

With this in mind, the idea of creating a 'runtime services layer' was
hatched. This would take the form of a framework within OMPI, through which
all runtime functionality would be accessed. This would allow new or
different runtime systems to be used with Open MPI. Additionally, with such a
system it would be possible to have multiple versions of open rte coexisting,
which may facilitate development and testing. Finally, this would solidify the
interface between OMPI and the runtime system, as well as provide
documentation and side effects of each interface function.

However, such a change would be fairly invasive to the OMPI layer, and
needs a buy-in from everyone for it to be possible.

Here is a summary of the changes required for the RSL (at least how it is
currently envisioned):

1. Add a framework to ompi for the rsl, and a component to support orte.
2. Change ompi so that it uses the new interface. This involves:
         a. Moving runtime specific code into the orte rsl component.
         b. Changing the process names in ompi to an opaque object.
         c. change all references to orte in ompi to be to the rsl.
3. Change the configuration code so that open-rte is only linked where needed.

Of course, all this would happen on a tmp branch.

The design of the rsl is not solidified. I have been playing in a tmp branch
(located at which everyone is
welcome to look at and comment on, but be advised that things here are
subject to change (I don't think it even compiles right now). There are
some fairly large open questions on this, including:

1. How to handle mpirun (that is, when a user types 'mpirun', do they
always get ORTE, or do they sometimes get a system specific runtime). Most
likely mpirun will always use ORTE, and alternative launching programs would
be used for other runtimes.
2. Whether there will be any performance implications. My guess is not,
but am not quite sure of this yet.

Again, I am interested in people's comments on whether they think adding
such abstraction is good or not, and whether it is reasonable to do such a
thing for v1.3.


Tim Prins