[slurm-users] Advice on setting a partition QOS

David Baker D.J.Baker at soton.ac.uk
Wed Sep 25 12:12:23 UTC 2019


I have defined a partition and corresponding QOS in Slurm. This is the serial queue to which we route jobs that require up to (and including) 20 cpus. The nodes controlled by serial are shared. I've set the QOS like so..

[djb1 at cyan53 slurm]$ sacctmgr show qos serial format=name,maxtresperuser
      Name     MaxTRESPU
---------- -------------
    serial       cpu=120

The max cpus/user is set high to try to ensure (as often as possible) that the nodes are all busy and not in mixed states. Obviously this cannot be the case all the time -- depending upon memory requirements, etc.

I noticed that a number of jobs were pending with the reason QOSMaxNodePerUserLimit. I've tried firing test jobs to the queue myself and noticed that I can never have more than 32 jobs running (each requesting 1 cpu) and the rest are pending as per the reason above. Since the QOS cpu/user limit is set to 120 I would expect to be able to run more jobs -- given that some serial nodes are still not fully occupied. Furthermore, I note that other users appear not to be able to use more then 32 cpus in the queue.

The 32 limit does make a degree of sense. The "normal" QOS is set to cpus/user=1280, nodes/user=32. It's almost like the 32 cpus in the serial queue are being counted as nodes -- as per the pending reason.

Could someone please help me understand this issue and how to avoid it?

Best regards,
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