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Subject: [OMPI devel] RTE node allocation component
From: Alex Margolin (alex.margolin_at_[hidden])
Date: 2012-04-13 12:07:15


Hi,

The next component I'm writing is a component for allocating nodes to
run the processes of an MPI job.
Suppose I have a "getbestnode" executable which not only tells me the
best location for spawning a new process,
but it also reserves the space (for some time), so that every time I run
it I get different results (as the best cores are already reserved).

I thought I should write a component under orte/mca/ras, similar to
loadleveler, but the problem is that I can't determine inside the module
the amount of slots required allocate. It gets an list to fill in as a
parameter, and
I guess it assumes I somehow know how many processes are run because the
allocation was done externally and now I'm just asking the allocator for
the list.

A related location, the rmaps, has this information (and much more), but
it doesn't look like a good location for such a module since it maps
already allocated resources, and has a lot of irrelevant code in this case.

Maybe the answer is to change the base module a bit, to contain this
information? It could be used as a decent sanity check for other modules
- making sure the external allocation fits the amount of processes we
intend to run. Maybe orte_ras_base_allocate(orte_job_t *jdata) in
ras_base_allocate.c can store the relevant information from jdata in
orte_ras_base? In the long run it can become a parameter passed to the
ras components, but for backwards-compatability the global will do for now.

Thanks,
Alex

P.S. An RDS component is elaborately mentioned in ras.h, yet it is no
longer available, right?