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ULHPC Slurm QOS 2.0

Quality of Service or QOS is used to constrain or modify the characteristics that a job can have. This could come in the form of specifying a QoS to request for a longer run time or a high priority queue for a given job.

To select a given QOS with a Slurm command, use the --qos <qos> option:

srun|sbatch|salloc|sinfo|squeue... [-p <partition>] --qos <qos> [...]

The default QoS of your jobs depends on your account and affiliation. Normally, the --qos <qos> directive does not need to be set for most jobs

We favor in general cross-partition QOS, mainly tied to priority level (low \rightarrow urgent). A special preemptible QOS exists for best-effort jobs and is named besteffort.

Available QOS

QOS (partition) Prio GrpTRES MaxTresPJ MaxJobPU MaxWall
besteffort (*) 1 50
low (*) 10 2
normal (*) 100 50
long (*) 100 node=6 node=2 4 14-00:00:00
debug (interactive) 150 node=8 10
high (*) 200 50
urgent (*) 1000 100

List QOS Limits

Use the sqos utility function to list the existing QOS limits.

List current ULHPC QOS limits with sqos

$ sqos
\# sacctmgr show qos  format="name%20,preempt,priority,GrpTRES,MaxTresPerJob,MaxJobsPerUser,MaxWall,flags"
                Name    Preempt   Priority       GrpTRES       MaxTRES MaxJobsPU     MaxWall                Flags
-------------------- ---------- ---------- ------------- ------------- --------- ----------- --------------------
              normal besteffort        100                                    50                      DenyOnLimit
          besteffort                     1                                   100                        NoReserve
                 low besteffort         10                                     2                      DenyOnLimit
                high besteffort        200                                    50                      DenyOnLimit
              urgent besteffort       1000                                   100                      DenyOnLimit
               debug besteffort        150        node=8                      10                      DenyOnLimit
                long besteffort        100        node=6        node=2         4 14-00:00:00 DenyOnLimit,Partiti+

What are the possible limits set on ULHPC QOS?

At the QOS level, the following elements are composed to define the resource limits for our QOS:

  • Limits on Trackable RESources (TRES - a resource (cpu,node,etc.) tracked for usage or used to enforce limits against), in particular:
    • GrpTRES: The total count of TRES able to be used at any given time from jobs running from the QOS.
      • If this limit is reached new jobs will be queued but only allowed to run after resources have been relinquished from this group.
    • MaxTresPerJob: the maximum size in TRES (cpu,nodes,...) any given job can have from the QOS
  • MaxJobsPerUser: The maximum number of jobs a user can have running at a given time
  • MaxWall[DurationPerJob]= The maximum wall clock time any individual job can run for in the given QOS.

As explained in the Limits section, there are basically three layers of Slurm limits, from least to most priority:

  1. None
  2. partitions
  3. account associations: Root/Cluster -> Account (ascending the hierarchy) -> User
  4. Job/Partition QOS

Last update: April 19, 2024