[jsdl-wg] Process Topology

[Karl Czajkowski]

Chris:

One concern I have is that in typical use with GRAM our users expect a
certain number of job processes to be launched across all
resources. In other words, their typical job is a fixed-layout
SPMD-style executable or a master/slave executable and they do not do
any explicit process startup in the program.

I am nearly certain that we pass the GRAM "count" attribute as the
allocation parameter (-n in your example) to the local scheduler but
depending on the value of our jobType=single|multi|mpi attribute we
also construct a job script which does the launching of all processes.
We also have a "hostCount" which we use to sort out SMP allocation
issues in a simple round-robin fashion.  So, we view a single set of
declarative parameters as having a projection into both allocation and
job-control functions.

We do not handle fancier topology options except through some
site-specific extensions that people have tried. I am not sure what
your note means when it says to allocate "as a unit", so I'd like
clarification on that before we move on.

I think it is a little too extreme to say JSDL shouldn't express job
process topology.  That seems just important to me as resource
topology, and the "isomorphism" or mapping between the two is also
important.  What you rightly point out is that the operational
behavior to _get_ the mapping is dependent on some combination of the
job and local scheduler runtime environments, e.g. does the manager or
the job take care of task launch.

I never much liked our jobType attribute, but it is there because this
problem had to be addressed somehow. I would accept an alternate
rendering where separate logical managers accepted a homogeneous job
type and had a fixed behavior, so this would be implicit context. This
would also better handle the esoteric "which mpirun to use" problem we
can have with "mpi" type jobs on systems with native MPI and MPICH-G,
etc.

So to reiterate: shouldn't JSDL express job process topology or
mapping into resources even if it is underspecified "how" the
processes will get that way?  Is it necessary to express two
topologies, or just to expect that they have identical expression in
one place in JSDL, and it requires context and/or extended content to
define how the processes get that way?


karl

-- 
Karl Czajkowski
karlcz at univa.com