My concern was you config inadvertantly having that line commented out and then seeing problems. If it wasn't then no worries at this point.

We run using preempt/partition_prio on our cluster and have a mix of partitions using PreemptMode=OFF and PreemptMode=REQUEUE. So I know that combination works. I would be surprised if PreemptMode=CANCEL did not work as that's a valid option.

Something we do have set though is what the default mode is. We have set:

### Govern's default preemption behavior
PreemptType=preempt/partition_prio
PreemptMode=REQUEUE

So you might try setting that default of PreemptMode=CANCEL and then set specific PreemptModes for all your partitions. That's what we do and it works for us.

-Paul Edmon-

On 1/12/2024 10:33 AM, Davide DelVento wrote:

Thanks Paul,

I don't understand what you mean by having a typo somewhere. I mean, that configuration works just fine right now, whereas if I add the commented out line any slurm command will just abort with the error "PreemptType and PreemptMode values incompatible". So, assuming there is a typo, it should be in the commented line right? Or are you saying that having that line makes slurm sensitive to a typo somewhere else that would be otherwise ignored? Obviously I can't exclude that option, but it seems unlikely to me. Also because it does say these two things are incompatible. 

It would obviously much better if the error would say what EXACTLY is incompatible with what, but the documentation at https://slurm.schedmd.com/preempt.html I see many clues of what that could be, and hence I am asking people here who may have deployed preemption already on their system. Some excerpts from that URL:

PreemptType: Specifies the plugin used to identify which jobs can be preempted in order to start a pending job.

• preempt/none: Job preemption is disabled (default).
• preempt/partition_prio: Job preemption is based upon partition PriorityTier. Jobs in higher PriorityTier partitions may preempt jobs from lower PriorityTier partitions. This is not compatible with PreemptMode=OFF.

which somewhat make it sounds like all partitions should have preemption set and not only some? I obviously have some "off" partitions. However elsewhere in that document it says

PreemptMode: Mechanism used to preempt jobs or enable gang scheduling. When the PreemptType parameter is set to enable preemption, the PreemptMode in the main section of slurm.conf selects the default mechanism used to preempt the preemptable jobs for the cluster.
PreemptMode may be specified on a per partition basis to override this default value if PreemptType=preempt/partition_prio.

which kind of sounds like it should be okay (unless it means **everything** must be different than OFF). Yet still elsewhere in that same page it says

On the other hand, if you want to use PreemptType=preempt/partition_prio to allow jobs from higher PriorityTier partitions to Suspend jobs from lower PriorityTier partitions, then you will need overlapping partitions, and PreemptMode=SUSPEND,GANG to use Gang scheduler to resume the suspended job(s). In either case, time-slicing won't happen between jobs on different partitions.

Which somewhat sounds like only suspend and gang can be used as preemption modes, and not cancel (my preference) or requeue (perhaps acceptable, if I jump through some hoops).

So to me the documentation is highly confusing about what can or cannot be used together with what else, and the examples at the bottom of the page are nice, but they do not specify the full settings. Particularly this one https://slurm.schedmd.com/preempt.html#example2 is close enough to mine, but it does not tell what PreemptType has been chosen (nor if "cancel" would be allowed or not in that setup).

Thanks again!

On Fri, Jan 12, 2024 at 7:22 AM Paul Edmon <pedmon@cfa.harvard.edu> wrote:

At least in the example you are showing you have PreemptType commented out, which means it will return the default. PreemptMode Cancel should work, I don't see anything in the documentation that indicates it wouldn't.  So I suspect you have a typo somewhere in your conf.

-Paul Edmon-

On 1/11/2024 6:01 PM, Davide DelVento wrote:

I would like to add a preemptable queue to our cluster. Actually I already have. We simply want jobs submitted to that queue be preempted if there are no resources available for jobs in other (high priority) queues. Conceptually very simple, no conditionals, no choices, just what I wrote.

However it does not work as desired.

This is the relevant part:

grep -i Preemp /opt/slurm/slurm.conf
#PreemptType = preempt/partition_prio
PartitionName=regular DefMemPerCPU=4580 Default=True Nodes=node[01-12] State=UP PreemptMode=off PriorityTier=200
PartitionName=All DefMemPerCPU=4580 Nodes=node[01-36] State=UP PreemptMode=off PriorityTier=500
PartitionName=lowpriority DefMemPerCPU=4580 Nodes=node[01-36] State=UP PreemptMode=cancel PriorityTier=100


That PreemptType setting (now commented) fully breaks slurm, everything refuses to run with errors like

$ squeue
squeue: error: PreemptType and PreemptMode values incompatible
squeue: fatal: Unable to process configuration file

If I understand correctly the documentation at https://slurm.schedmd.com/preempt.html that is because preemption cannot cancel jobs based on partition priority, which (if true) is really unfortunate. I understand that allowing cross-partition time-slicing could be tricky and so I understand why that isn't allowed, but cancelling? Anyway, I have to questions:

1) is that correct and so should I avoid using either partition priority or cancelling?

2) is there an easy way to trick slurm into requeing and then have those jobs cancelled instead?

3) I guess the cleanest option would be to implement QoS, but I've never done it and we don't really need it for anything else other than this. The documentation looks complicated, but is it? The great Ole's website is unavailable at the moment...

Thanks!!