[torquedev] nodes, procs, tpn and ncpus

Martin Siegert siegert at sfu.ca
Thu Jun 10 12:27:01 MDT 2010


On Wed, Jun 09, 2010 at 06:01:31PM -0700, Garrick Staples wrote:
> On Wed, Jun 09, 2010 at 08:52:08PM -0400, Glen Beane alleged:
> > On Wed, Jun 9, 2010 at 8:31 PM, Garrick Staples <garrick at usc.edu> wrote:
> > > I know I'm getting in on this conversation late, but here is my fantasy:
> > >
> > > nodes=X gives X number of cpus. Packed. Your job is CPU bound and you don't
> > > care how they are packed.
> > 
> > blah.  that is overloading the meaning of nodes.  I like the new
> > procs=X instead. It basically means the same thing,  you get X
> > processors, moab seems to pack them on as few nodes as possible.
> > TORQUE doesn't do anything with procs yet...
> 
> Nothing is overloaded. "nodes" has always translated to "vnodes" inside of
> torque. If you don't specify ppn, then you don't care about where your
> processors land. Perfectly logical. This case also covers the vast majority of
> jobs.

I am with Glen: nodes=X is just an abbreviation for nodes=X:ppn=1 - it alwasy
has been that way. That ppn=1 means "packed" is totally counterintuitive
- none of our users ever understood this this way. We were actually forced
to set EXACTNODE because that is the syntax users expect from specifying
processors-per-node. This is not about what we like, but about a sensible
user interface that is intuitive for users. Giving a user 5 processors on
the same node when specifying ppn=1 is not what users expect.

> > > nodes=X:ppn=Y gives you X unique nodes with Y cpus per machine. Not-packed.

This has not been that way: nodes=X:ppn=Y gave you any multiple of Y cpus
on a node, i.e., packed (and this includes the nodes=X (= nodes=X:ppn=1)
case.

> > > This lets you spread IO around because you know you need it.
> > 
> > 
> > 
> > here is what I want
> > 
> > procs=X gives you X processors, user doesn't care about layout (hack that
> > works with Moab, should be made to work properly with pbs_sched/qrun)
> > nodes=X:ppn=Y gives you exactly X unique nodes with Y processors per node
> > nodes=X - I'm not sure about this one, but to preserve historic behavior I
> > think TORQUE should give you X nodes with one processor on each node (Moab
> > can have an option to treat it like procs=X, which is the current behavior)
> > _______________________________________________ torquedev mailing list

Agreed. This is what we want as well.

> Getting torque to jive procs with nodes is a lot more work.
> 
> My plan is easy, simple, and I think covers everyone's use cases.

It does not cover our use cases. Furthermore, having ppn not mean
processors-per-node results in a never ending support problem.

> Everyone has always wanted "gimme X cores, anywhere". The solution is to not
> use EXACTNODE and "nodes=X" does what you want. But EXACTNODE breaks the
> "nodes=X:ppn=y" case. If we just change maui/moab to not pack jobs with ppn,
> then we are done.

That is not a solution. If we not set EXACTNODE, then users who need
nodes=N:ppn=1 (in its very meaning, namely exactly one processor per
node) cannot be satisfied. And if we do set EXACTNODE, there is no way
(other than procs) to request N processors anywhere. This is the reason
why procs was introduced in the first place: so that we can set EXACTNODE
and satisfy both type of requests.

Cheers,
Martin

-- 
Martin Siegert
Head, Research Computing
WestGrid Site Lead
IT Services                                phone: 778 782-4691
Simon Fraser University                    fax:   778 782-4242
Burnaby, British Columbia                  email: siegert at sfu.ca
Canada  V5A 1S6


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