[slurm-users] Slurm very rarely assigned an estimated start time to a job

David Rhey drhey at umich.edu
Thu Oct 3 19:37:02 UTC 2019

We've been working to tune our backfill scheduler here. Here is a
presentation some of you might have seen at a previous SLUG on tuning the
backfill scheduler. HTH!



On Wed, Oct 2, 2019 at 1:37 PM Mark Hahn <hahn at mcmaster.ca> wrote:

> >(most likely in the next year). My reaction is that Slurm very rarely
> >provides an estimated start time for a job. I understand that this is not
> >possible for jobs on hold and dependent jobs.
> it's also not possible if both running and queued jobs
> lack definite termination times; do yours?
> my understanding is the following:
> the main scheduler does not perform forward planning.
> that is, it is opportunistic.  it walks the list of priority-sorted
> pending jobs, starting any which can run on currently free
> (or preemptable) resources.
> the backfill scheduler is a secondary, asynchronous loop that tries hard
> not to interfere with the main scheduler (severely throttles itself)
> and tries to place start times for pending jobs.
> the main issue with forward scheduling is that if high-prio jobs become
> runnable (submitted, off hold, dependency-satisfied), then most of the
> (tentative) start times probably need to be removed.
> a quick look at plugins/sched/backfill/backfill.c indicates that things
> are /complicated/ ;)
> we (ComputeCanada) don't see a lot of forward start times either.
> I also would welcome discussion of how to tune the backfill scheduler!
> I suspect that in order to work well, it needs a particular distribution
> of job priorities.
> regards, mark hahn.

David Rhey
Advanced Research Computing - Technology Services
University of Michigan
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