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From: Tim Prins (tprins_at_[hidden])
Date: 2007-08-19 18:49:34


On Friday 17 August 2007 08:40:01 am Jeff Squyres wrote:
> I am definitely interested to see what the RSL turns out to be; I
> think it has many potential benefits. There are also some obvious
> issues to be worked out (e.g., mpirun and friends).
Yeah, thinking through this and talking to others, it seems like the best way
to deal with this is to say that mpirun points to our default runtime (orte),
and that to use any other rsl component, you have to use that system's
specific launcher (could be a 'srun', or a 'mpirun-foobar', whatever the
system wants to do).

>
> As for whether this should go in v1.3, I don't know if it's possible
> to say yet -- it will depend on when RSL becomes [at least close to]
> ready, what the exact schedule for v1.3 is (which we've been skittish
> to define, since we're going for a feature-driven release), etc.

I agree that it is impossible to say right now, but wanted to throw it out
there for people to consider/think about.

Tim

>
> On Aug 16, 2007, at 9:47 PM, Tim Prins wrote:
> > 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 https://svn.open-mpi.org/svn/ompi/tmp/rsl) 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.
> >
> > Thanks,
> >
> > Tim Prins
> > <RSL-Diagram.pdf>
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