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Queues and Charges

This page details the QOS and queue usage policies. Examples for each type of slurm job are available.

When a job runs on a NERSC supercomputer, charges accrue against one of the user's projects. The unit of accounting for these charges is the "Node Hour", based on the performance of the nodes on Perlmutter. The total number of charged hours for a job is a function of:

  • the number of nodes and the walltime used by the job,
  • the QOS of the job, and
  • the "charge factor" for the system upon which the job was run.

Job charging policies, including the intended use of each queue, are outlined in more detail under "Policies". This page summarizes the limits and charges applicable to each queue.

Selecting a Queue

Jobs are submitted to different queues depending on the queue constraints and the user's desired outcomes. Each queue corresponds to a "Quality of Service" (QOS): Each queue has a different service level in terms of priority, run and submit limits, walltime limits, node-count limits, and cost. At NERSC, the terms "queue" and "QOS" are often used interchangeably.

Most jobs are submitted to the "regular" queue. A user who needs fast turnaround while they are using the large telescope could prearrange with NERSC to use the realtime queue for these runs. The user with the scientific emergency will incur a higher-than-regular charge, while a user who can be flexible about their required runtime is rewarded with a substantial discount.

Note

The "debug" queue is the default queue on Perlmutter and will be applied to any job for which a QOS is not specified.

Assigning Charges

Users who are members of more than one project can select which one should be charged for their jobs by default. In Iris, under the "Compute" tab in the user view, select the project you wish to make default.

To charge to a non-default project, use the -A projectname flag in Slurm, either in the Slurm directives preamble of your script, e.g.,

#SBATCH -A myproject

or on the command line when you submit your job, e.g., sbatch -A myproject ./myscript.sl.

Warning

For users who are members of multiple NERSC projects, charges are made to the default project, as set in Iris, unless the #SBATCH --account=<NERSC project> flag has been set.

Calculating Charges

The cost of a job is computed in the following manner: $$ \text{walltime in hours} \times \text{number of nodes} \times \text{QOS factor} \times \text{charge factor} $$.

Example

The charge for a job that runs for 40 minutes on 3 CPU nodes in the preempt QOS (QOS factor of 0.5) would be calculated $$ \frac{40\ \text{mins}}{60\ \text{min/hr}} \times 3\ \text{nodes} \times 0.5 \times 1\ \text{charged-hours/node-hour} = \frac{2}{3} \times 3 \times 0.5 \times 1 = 1.0\ \text{charged hours}.$$

Example

A job which ran for 35 minutes on 3 GPU nodes on Perlmutter with the regular QOS would be charged: $$ \frac{35}{60}\ \text{hours} \times 3\ \text{nodes} \times 1 = 1.75\ \text{charged hours} $$

Note

Jobs in the "shared" QOS are only charged for the fraction of the node used.

Example

A job which ran for 10 hours on 2 GPUs in the shared QOS on Perlmutter GPU would be charged: $$ 10\ \text{hours} \times (2 \text{GPUs}/4) \times 1 = 5\ \text{charged hours} $$

Note

Jobs are charged according to the resources they made unavailable for other jobs, i.e., the number of nodes reserved (regardless of use) and the actual walltime used (regardless of the specified limit).

Charge Factors

Charge factors on Perlmutter are based on the performance of the Perlmutter nodes and are therefore equal to one. Future systems may have different charge factors.

Architecture Charge Factor
Perlmutter CPU 1
Perlmutter GPU 1

Note

Perlmutter GPU and CPU allocations are separate pools that can be used only on the respective resource and cannot be exchanged.

QOS Cost Factor: Charge Multipliers and Discounts

The QOS cost factor is a function of which queue a job runs in. Jobs in the preempt queue, on the other hand, receive a substantial discount in exchange for flexibility about walltime, and jobs in the overrun queue run free of charge.

QOS QOS Factor Conditions
regular 1 (standard charge factor)
overrun 0 available only when allocation is exhausted
preempt 0.25 or 0.5 guaranteed 2-hr minimum walltime, then subject to preemption

QOS Limits and Charges

Perlmutter GPU

QOS Max nodes Max time (hrs) Submit limit Run limit Priority QOS Factor Charge per Node-Hour
regular - 24 5000 - medium 1 1
interactive 4 4 2 2 high 1 1
shared_interactive 0.5 4 2 2 high 1 1
jupyter 4 6 1 1 high 1 1
debug 8 0.5 5 2 medium 1 1
shared1 0.5 24 5000 - medium 1 11
preempt 128 24 (preemptible after two hours) 5000 - medium 0.25 0.25
debug_preempt 2 0.5 (preemptible after five minutes) 5 2 medium 0.25 0.25
overrun - 24 (preemptible after two hours) 5000 - very low 0 0
shared_overrun 0.5 24 (preemptible after two hours) 5000 - very low 0 0
realtime custom custom custom custom very high 1 1

  • The "debug" QOS is the default.

  • Nodes allocated by a "regular" QOS job are exclusively used by the job.

  • Jobs in the preemptible QOS can be preempted after two hours. Jobs can be automatically requeued after preemption using the --requeue sbatch flag. See the Preemptible Jobs section for details.

  • NERSC's Jupyter service uses the "jupyter" QOS to start JupyterLab on compute nodes. Other uses of the QOS are currently not authorized, and the QOS is monitored for unauthorized use.

  • Jobs may run on the "standard" Perlmutter GPU nodes or on the subset of GPU nodes which have double the GPU-attached memory. To specifically request these higher-bandwidth memory nodes, use -C gpu&hbm80g in your job script instead of -C gpu. Jobs with this constraint must use 256 or fewer nodes.

Shared GPU Jobs

GPU jobs in the shared QOS may request 1 or 2 GPUs and will be allocated a corresponding 16 CPU cores and 64 GB RAM or 32 CPU cores and 128 GB RAM, respectively.

Perlmutter CPU

QOS Max nodes Max time (hrs) Submit limit Run limit Priority QOS Factor Charge per Node-Hour
regular - 24 5000 - medium 1 1
interactive 4 4 2 2 high 1 1
shared_interactive 0.5 4 2 2 high 1 1
jupyter 4 6 1 1 high 1 1
debug 8 0.5 5 2 medium 1 1
shared1 0.5 24 5000 - medium 1 11
preempt 128 24 (preemptible after two hours) 5000 - medium 0.5 0.5
debug_preempt 2 0.5 (preemptible after five minutes) 5 2 medium 0.5 0.5
overrun - 24 (preemptible after two hours) 5000 - very low 0 0
shared_overrun 0.5 24 (preemptible after two hours) 5000 - very low 0 0
realtime custom custom custom custom very high 1 1

  • The "debug" QOS is the default.

  • Nodes allocated by a "regular" QOS job are exclusively used by the job.

  • Even though there is no node limit for the regular queue, not all of the projected 3072 nodes are available today. Please check the state of the nodes in the regular queue with sinfo -s -p regular_milan_ss11

  • Jobs in the preemptible QOS can be preempted after two hours. Jobs can be automatically requeued after preemption using the --requeue sbatch flag. See the Preemptible Jobs section for details.

  • NERSC's Jupyter service uses the "jupyter" QOS to start JupyterLab on compute nodes. Other uses of the QOS are currently not authorized, and the QOS is monitored for unauthorized use.

Perlmutter Login

QOS Max nodes Max time (hrs) Submit limit Run limit Priority QOS Factor Charge per Node-Hour
xfer 1 (login) 48 100 15 low - 0
cron 1/128 (login) 24 - - low - 0
workflow 0.25 (login) 2160 - - low - 0

Discounts

Several QOS's offer reduced charging rates:

  • The "preempt" QOS is charged 50% of the "regular" QOS on CPU nodes and 25% of "regular" QOS on GPU nodes, with a minimum walltime of two hours guaranteed.
  • The "overrun" QOS is free of charge and is only available to projects that are out of allocation time. Please refer to the overrun section for more details.

  1. Shared jobs are only charged for the fraction of the node resources used. ↩↩↩↩

  2. Batch job submission is not enabled and the 64-node limit applies per project not per user. ↩