[GE users] resource reservation not working

Ross Dickson Ross.Dickson at dal.ca
Wed Sep 26 14:15:20 BST 2007

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Hello, Grid Engineers.

I think I was mistaken about reservation not working --- It just doesn't
work the way I thought it would.  What I expected was that, as resources
(slots) came free, the scheduler would set them aside for the reserving job
until it had accumulated enough to run it.  Instead what happens is that the
scheduler picks an arbitrary list of nodes that may *or may not* have free
slots, and sets those slots aside as they come free.  If slots come free
that are *not* on this preselected list, they are cheerfully assigned to 
jobs, even those of lower priority than the reserving job.

The indirect evidence of this was right there in the monitor file
($SGE_ROOT/$SGE_CELL/common/schedule) when I had it turned on, but
I looked right past it:  The reserving job has a list of queue instances 
with it:

3568:1:RESERVING:1190724115:660:Q:all.q at cl023:slots:1.000000
3568:1:RESERVING:1190724115:660:Q:all.q at cl026:slots:1.000000

...and the list never changes!   I suspect now that what happened 
earlier was
that a node *not* on the reserved list came free, and the job I thought was
violating the reservation policy was scheduled there.  That's certainly what
happened with some jobs that were scheduled last night.

I suppose there ought to be a request-for-enhancement about this:  If
the scheduler were smart enough to glom resources *as they became 
rather than preselecting them (who knows how?), then reservation would
probably be a more effective function.

Ross Dickson         HPC Consultant
ACEnet               http://www.ace-net.ca
+1 902 494 6710      Skype: ross.m.dickson

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