[slurm-users] Quickly throttling/limiting a specific user's jobs

Paul Edmon pedmon at cfa.harvard.edu
Wed Sep 23 00:01:33 UTC 2020

I would look at:

/MaxJobs/=<max jobs>
    Maximum number of jobs each user is allowed to run at one time in
    this association. This is overridden if set directly on a user.
    Default is the cluster's limit. To clear a previously set value use
    the modify command with a new value of -1. 

Which is Association based.  So you could just modify their account 
directly and set it to something low.

You can also simply put their pending jobs in hold state.  That way they 
won't be considered for scheduling but won't be outright removed.  
Setting fairshare to 0 has the same effect.

-Paul Edmon-

On 9/22/2020 7:58 PM, Brian Andrus wrote:
> Well, I know of no way to 'throttle' running jobs. Once they are out 
> the gate, you can't stop them from leaving..
> That said, your approach of setting arraytaskthrottle is just what you 
> want for any pending jobs.
> As a preventative measure, I imagine you could set the default to 1 
> and then change it with a job_submit script.
> As far as currently running tasks, well, you have to figure that. You 
> could kill/requeue them, but that can break things for the user. If 
> their code supports it, they could checkpoint/restart as part of the 
> process.
> You can suspend them, but they still sit on the node waiting to be 
> resumed, but the node resources may get assigned to other jobs while 
> they wait to resume.
> Brian Andrus
> On 9/22/2020 2:33 PM, Ransom, Geoffrey M. wrote:
>> Hello
>>    We had a user post a large number of array jobs with a short 
>> actual run time (20-80 seconds, but mostly to the low end) and 
>> slurmctld was falling behind on RPC calls trying to handle the jobs. 
>> It was a bit awkward trying to slap arraytaskthrottle=5 on each of 
>> the queued array jobs while slurmctld was having issues handling the 
>> RPC load.
>> I’m looking to make a QOS with MaxJobsPerUser=50 set that I can 
>> quickly add to a user to throttle their jobs but..
>> 1)Adding a QOS to the user does not affect queued jobs so I still 
>> have to get all of the users jobids and modify each on directly.
>> 2)I queued up a test job with the QOS set and it is still running 100 
>> jobs at a time (what I set arraytaskthrottle to in the job) and not 
>> limiting the “user” to 50 jobs.
>> 3)I tried adding the FLAG OverPartQOS to see if that changed the 
>> behavior, but it did not seem to do anything. My test cluster I ran 
>> this on doesn’t have any other QOSes defined but our production 
>> cluster does have a partition QOS in place limiting single users to 
>> about 80% of the CPUs with MaxTRESPerUser.
>> Is there a quick way to limit how many jobs a specific user can run 
>> at one time on the cluster or in a partition if we need to throttle 
>> them back in an emergency but we don’t want to flat out kill their jobs?
>> Thanks.
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