SLURM/Priority

SLURM at UMIACS is configured to prioritize jobs based on a number of factors, termed multifactor priority in SLURM. Each job submitted to the scheduler is assigned a priority value, which can be viewed in the output of scontrol show job <jobid>:

$ scontrol show job 1
JobId=1 JobName=bash
   UserId=username(13337) GroupId=username(13337) MCS_label=N/A
   Priority=10841 Nice=0 Account=nexus QOS=default
...

Pending Jobs

If the partition that you submit your job to cannot instantly begin your job due to no compute node(s) having the resources free to run it, your job will remain in the Pending state with the listed reason (Resources). If there is another job already pending with this reason and you submit a job to the same partition that gets assigned lower priority, your job will remain in the Pending state with reason (Priority). The scheduler will only begin execution of a lower priority job if starting the job would not push the begin times for any higher priority jobs (in the same partition) further back.

Lowering some combination of the resources you are requesting and/or the time limit may allow submitted jobs to run more quickly or instantly during times where a partition is under resource pressure. The command squeue -j <jobid> --start> can be used to provide a time estimate for when your job will start. We are also actively developing a new command alias to quickly aggregate the free resources across all nodes that meet a given set of submission arguments to provide a better idea of what jobs may begin sooner. We will announce this to the Nexus user community and mention it on this page when it is deployed on the cluster.

Priority Factors

The priority factors in use at UMIACS include:

• Age of job i.e. time spent waiting to run in the queue
• Partition job was submitted to
• Fair-share of resources
• "Nice" value that job was submitted with

Age

The longer a job is eligible to run but cannot, the higher the job's priority becomes as it continue to wait in the queue. The priority modifier for this factor reaches its limit after 7 days.

Partition

The partition named scavenger on each of our clusters always has a lower priority factor for its jobs than all other partitions on that cluster. As mentioned in other UMIACS cluster-specific documentation, jobs submitted to this partition are also preemptable. These two design choices give the partition its name; jobs submitted to the scavenger partition "scavenge" for available resources on the cluster rather than consume dedicated chunks of resources, and are interrupted by jobs seeking to consume dedicated chunks of resources.

On Nexus, labs/centers may also have their own scavenger partitions (<labname>-scavenger) if the faculty for the lab/center have decided upon some sort of limit on jobs (number of simultaneous jobs, number of actively consumed billing resources, etc.) in their non-scavenger partitions. These lab/center scavenger partitions allow for more jobs to be run by members of that lab/center on that lab's/center's nodes only, but are preemptable by that lab's/center's non-scavenger partition jobs.

In decreasing order of priority (highest first), our job priorities for partitions are:

1. Lab/center non-scavenger partitions
2. Lab/center scavenger partitions
3. Cluster-wide scavenger partitions

Fair-share

The more resources your jobs have already consumed within an account, the lower priority factor your future jobs will have when compared to other users' jobs in the same account who have used fewer resources (so as to "fair-share" with other users). Additionally, if there are multiple accounts that can submit to a partition, and the sum of resources of all users' jobs within account A is greater than the sum of resources of all users' jobs within account B, the lower priority factor all future jobs from users in account A will have when compared to all future jobs from users in account B. (In other words, fair-share is hierarchical.)

You can view the various fair-share statistics with the command sshare -l. It will show your specific FairShare values (always between 0.0 and 1.0) within accounts that you have access to. You can also view other accounts' Level Fairshare (LevelFS).

Account                    User  RawShares  NormShares    RawUsage   NormUsage  EffectvUsage  FairShare    LevelFS                    GrpTRESMins                    TRESRunMins
-------------------- ---------- ---------- ----------- ----------- ----------- ------------- ---------- ---------- ------------------------------ ------------------------------
root                                          0.000000 66034847484                  1.000000                                                      cpu=7746109,mem=69754856514,e+
 cbcb                                    1    0.032258 14115111102    0.213757      0.213757              0.150910                                cpu=4969,mem=20355003,energy=+
 class                                   1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 clip                                    1    0.032258  1568122041    0.023733      0.023733              1.359207                                cpu=70083,mem=1464478788,ener+
 cml                                     1    0.032258    17338485    0.000263      0.000263            122.854754                                cpu=29958,mem=245415936,energ+
 cml-abhinav                             1    0.032258      784250    0.000012      0.000012            2.7161e+03                                cpu=0,mem=0,energy=0,node=0,b+
 cml-cameron                             1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 cml-furongh                             1    0.032258  2098793815    0.031784      0.031784              1.014924                                cpu=940758,mem=8995575569,ene+
 cml-hajiagha                            1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 cml-john                                1    0.032258   258872094    0.003920      0.003920              8.228447                                cpu=476993,mem=5494963200,ene+
 cml-ramani                              1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 cml-scavenger                           1    0.032258  6734023027    0.101979      0.101979              0.316321                                cpu=1496736,mem=13036434773,e+
 cml-sfeizi                              1    0.032258   185510632    0.002809      0.002809             11.482444                                cpu=70732,mem=579442005,energ+
 cml-tokekar                             1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 cml-tomg                                1    0.032258    99040108    0.001500      0.001500             21.507603                                cpu=0,mem=0,energy=0,node=0,b+
 cml-zhou                                1    0.031250           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 gamma                                   1    0.032258  8880343229    0.134482      0.134482              0.239869                                cpu=2532358,mem=23460226867,e+
 mbrc                                    1    0.032258    27060567    0.000410      0.000410             78.716582                                cpu=0,mem=0,energy=0,node=0,b+
 mc2                                     1    0.032258        9175    0.000000      0.000000            2.3215e+05                                cpu=0,mem=0,energy=0,node=0,b+
 nexus                                   1    0.032258  3346084300    0.050672      0.050672              0.636599                                cpu=121941,mem=1468973003,ene+
  nexus                username          1    0.000779       69666    0.000001      0.000021   0.457407  37.435501                                cpu=0,mem=0,energy=0,node=0,b+
 scavenger                               1    0.032258 21762190063    0.329562      0.329562              0.097882                                cpu=1085904,mem=4775150199,en+
  scavenger            username          1    0.000779         171    0.000000      0.000000   0.033975 9.8885e+04                                cpu=0,mem=0,energy=0,node=0,b+
 vulcan                                  1    0.032258  1458631376    0.022089      0.022089              1.460352                                cpu=25968,mem=106368204,energ+
 vulcan-abhinav                          1    0.032258  4441051354    0.067254      0.067254              0.479648                                cpu=850445,mem=9471827285,ene+
 vulcan-djacobs                          1    0.032258   381503730    0.005777      0.005777              5.583472                                cpu=7656,mem=250882730,energy+
 vulcan-janus                            1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 vulcan-jbhuang                          1    0.032258    15619477    0.000237      0.000237            136.375587                                cpu=0,mem=0,energy=0,node=0,b+
 vulcan-lsd                              1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 vulcan-metzler                          1    0.032258   435471075    0.006595      0.006595              4.891520                                cpu=16235,mem=133000942,energ+
 vulcan-rama                             1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 vulcan-ramani                           1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+
 vulcan-yaser                            1    0.032258   209285667    0.003166      0.003166             10.189036                                cpu=15366,mem=251762005,energ+
 vulcan-zwicker                          1    0.032258           0    0.000000      0.000000                   inf                                cpu=0,mem=0,energy=0,node=0,b+

The actual resource weightings for the three main resources (memory per GB, CPU cores, and GPUs if applicable) are per-partition and can be viewed in the TRESBillingWeights line in the output of scontrol show partition. The billing value for a job is the sum of all resource weightings for resources the job has requested. This value is then multiplied by the amount of time a job has run in seconds to get the amount it contributes to the RawUsage for the association within the account it is running under.

There are two main algorithms we use for resource weightings:

Modern

This weighting algorithm is in use on the Nexus cluster. Resources have algorithmically computed floating point billing values, adjusted automatically as new resources are added to the cluster.

Modern: GPU-capable partitions

Each resource (memory/CPU/GPU) is given a weighting value such that their relative billings to each other are equal (33.33% each). The values are then rounded to whole numbers. Memory is typically always the most abundant resource by unit (weighting value of 1.0 per GB) and the CPU/GPU values are adjusted accordingly.

Different GPU types may also be weighted differently within the GPU relative billing. A baseline GPU type is first chosen. All GPUs of that type and other types that have lower FP32 performance (in TFLOPS) are given a weighting factor of 1.0. GPU types with higher FP32 performance than the baseline GPU are given a weighting factor calculated by dividing their FP32 performance by the baseline GPU's FP32 performance. The weighting values for each GPU type are then determined by normalizing the sum of all of GPU cards of different types multiplied by their weighting factors against the relative billing percentage for GPUs (33.33%).

The current baseline GPU is the NVIDIA RTX A4000.

Modern: CPU-only partitions

Each resource (memory/CPU) is first given a weighting value such that their relative billings to each other are equal (50% each). Memory is typically always the most abundant resource by unit (weighting value of 1.0 per GB) and the CPU value is adjusted accordingly. The final CPU weight value is then divided by 10, which ends up translating to roughly 90.9% of the billing weight being for memory and 9.1% being for CPU. This is done so as to not affect accounts' fair-share priority factors as much when running CPU-only jobs given the popularity of GPU computing.

Legacy

This weighting algorithm is currently in use on a few remaining standalone clusters for labs. Resources have fixed floating point billing values. Memory is billed at 0.125 per GB, CPU is billed at 1.0 per core, and GPU is billed at 4.0 per card.

Nice value

This is a submission argument that you as the user can include when submitting your jobs to deprioritize them. Larger values will deprioritize jobs more e.g.,

srun --pty --nice=2 bash

will have lower priority than

srun --pty --nice=1 bash

which will have lower priority than

srun --pty bash

assuming all three jobs were submitted at the same time. You cannot use negative values for this argument.