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-[[Category:SLURM]]
+#REDIRECT [[Account_and_QOS_limits_under_SLURM]]
-{{HPG2}}
-=Account and QOS Use=
-In the HiperGator 2.0 SLURM implementation a job's priority and resource limits are determined by its QOS (Quality of Service).  Every group with an HPG2 investment will have a corresponding SLURM '''account'''. Each SLURM account has two associated QOSs - the normal or high-priority '''main''' QOS and a low-priority '''burst''' QOS. In turn, each user who is a member of '''vested''' group i.e. a group with an investment and a corresponding computational allocation has a SLURM association. It is the association which determines which QOSs are a available to a user. In addition to the primary group association, users who have secondary group membership (in the Unix/Linux sense) will also have secondary group associations which will afford them access to the main and burst QOSs of that group's account.
-To see your SLURM associations, you can run the ''showAssoc'' command.  For example,
-<source lang=bash>
-$ showAssoc magitz
-              User    Account   Def Acct   Def QOS                                      QOS
------------------- ---------- ---------- --------- ----------------------------------------
-magitz                zoo6927      ufhpc     ufhpc zoo6927,zoo6927-b
-magitz                  ufhpc      ufhpc     ufhpc ufhpc,ufhpc-b
-magitz                 soltis      ufhpc    soltis soltis,soltis-b
-magitz                  borum      ufhpc     borum borum,borum-b
-</source>
-The output above shows that the user ''magitz'' has four SLURM associations and thus, access to 8 different QOSs.  By convention, a user's default account is always the account of their primary group.  Additionally, their default QOS is the main (high-priority) QOS.  If a user does not explicitly request a specific account and QOS, the user's default account and QOS will be assigned to the job.
-However, if the user ''magitz'' wanted to use the borum group's account (to which he has access by virtue of the borum account association), he would specify the account and the chosen QOS in his batch script as follows.
-<source lang=bash>
-    #SBATCH  --account=borum
-    #SBATCH  --qos=borum
-</source>
-or for the burst qos
-<source lang=bash>
-    #SBATCH  --account=borum
-    #SBATCH  --qos=borum-b
-</source>
-Note that both must be specified.  Otherwise, SLURM will assume the default '''ufhpc''' account is intended and the '''borum''' or '''borum-b''' QOSs will not be available to the job. Consequently, SLURM would deny the submission.
-These sbatch directives can also be given as command line arguments to "srun" as in,
-<source lang=bash>
-$ srun --account=borum --qos=borum-b some_command
-</source>
-==QOS Limits==
-SLURM refers to the resources (NCUs (cores), Memory (RAM), accelerators, software licenses, etc.) as '''Trackable Resources''' (TRES). The TRES available to a given group are determined by the group's investments and are limited by parameters assigned to the QOS.
-Continuing with the example above, we can see the trackable resource limits placed on the borum group's primary QOS by running,
-<source lang=bash>
-$ showQos borum
-                Name                          Descr                                       GrpTRES  GrpCPUs
--------------------- ------------------------------ --------------------------------------------- --------
-borum                borum qos                      cpu=41,mem=125952,gres/gpu=0,gres/mic=0             41
-</source>
-from which we can see that when submitting jobs under the borum group's primary QOS, users have access to a total of 41 cores, 125 GB of RAM with no access to accelerators (GPUs, MICs). These resource will be shared among all members of the borum group running jobs under the primary QOS.  Similarly, we can see the trackable resources available under the burst QOS with,
-<source lang=bash>
-$ showQos borum-b
-                Name                          Descr                                       GrpTRES  GrpCPUs
--------------------- ------------------------------ --------------------------------------------- --------
-borum-b              borum burst qos                cpu=369,mem=1133568,gres/gpu=0,gres/mic=0          369
-</source>
-There are additional limits and parameters associated with QOSs in addition to the TRES limits.  Among them are the maximum wall time available under the QOS and the base priority assigned to the job.  We can see this with,
-<source lang=bash>
-$ sacctmgr show qos format="name%-20,Description%-30,priority,maxwall" borum borum-b
-                Name                          Descr   Priority     MaxWall
--------------------- ------------------------------ ---------- -----------
-borum                borum qos                           36000 31-00:00:00
-borum-b              borum burst qos                       900  4-00:00:00
-</source>
-From which we see that main and burst QOS jobs are limited to a maximum duration of 31 and 4 days, respectively. Additionally, the base priority of a burst QOS job is 1/40th that of a main QOS job. It is important to remember that the base priority is only one component of the jobs overall priority and that the priority will change over time as the job waits in the queue.
-By policy, the burst QOS cpu and memory limits are always nine times (9x) those of the main QOS and are intended to allow groups to take advantage of unused resources beyond those that they have purchased for short periods of time.
-== Cores (CPUs) and Memory (RAM)==
-The resources of any computing device are limited. This is to say that the number of cores, the amount of memory, the memory bandwidth, the I/O bandwidth, etc. - all are limited. Once you have used up all of the available cores on a machine, it is fully consumed and unavailable to other users. This is true whether you use 1 byte of RAM or all of the RAM on the machine. Likewise, if your application uses all of the memory available to the machine, whether it uses 1 core or all the cores, the machine is consumed and unavailable to others. Because of this, we place limits on both the number of cores available to a group (based on the NCU investments) '''and''' the amount of memory available to a group (NCUs x 3GB).
-Why do we limit the amount of memory you can use? Because it is necessary to be fair to all investors. Consider a system where a PI has invested in 10 NCUs. His TRES cpu limit will be "10". With no memory limits he could submit ten jobs requesting 1 cpu and 120GB each. Because each machine only has about 120GB available for applications, each job would be started on a separate machine leaving no memory available for any other jobs to run on the machine. As a result the group has invested in 10 NCUS but is consuming 320. Such a scenario is not tenable and would quickly result in a grossly unfair allocation of resources. Thus, we place limits on both CPUs and memory.
-The total memory limit is calculated as 'QOS NCU * 3 GB'. For example, main QOS of 30 NCUs will have a group memory limit of 90gb while the burst qos for that group will be equal to '30 * 3gb * 9 = 810gb'. If the group memory limit is reached you will see a '(QOSGrpMemLimit)' status in the 'NODELIST(REASON)' column of the squeue output. For example,
-<source lang=bash>
- $ squeue | grep MemLimit | head -n 1
-    bigmem test_job   jdoe PD       0:00      1 (QOSGrpMemLimit)
-</source>
-The above message can only be seen in the output of the 'squeue' command and does not interfere with job submission. However, the job will not run and will remain in the pending state until the group falls below its memory limit.
-If the submitted job request so much memory or so many cores that either or both fall outside the total resource limit of the specified QOS, SLURM will refuse the job submission altogether and return the following error message,
-<source lang=bash>
-sbatch: error: Batch job submission failed: Job violates accounting/QOS policy
-               (job submit limit, user's size and/or time limits)
-</source>
-=Choosing QOS for a Job=
-When choosing between the main high-priority QOS and the 9x larger low-priority burst QOS you should start with the overall resource requirements for the job as for smaller allocations the main QOS might simply not be sufficiently large for some jobs whereas for other smaller jobs the wait time in the burst QOS could be too long. In addition, consider the current state of the account you are planning to use for your job. Use the ''slurm_info'' utility from the ''ufrc'' environment module to show the status of any SLURM account and the overall usage of HiPerGator resources to help you determine the best QOS for the job. For example, the following output from slurm_info shows that the main QOS for the ''ufgi'' account is actively used and only 19 cores out of 100 and 204gb out of the maximum 300gb are currently available whereas the burst QOS is unused. Furthermore, the total HiPerGator use is at 76%, which means that there's still available capacity from which burst resources can be drawn. In this case a job submitted to the '''ufgi-b''' qos should be able to start within a reasonable amount of time and will enjoy access to much larger amount of computational and memory resources. If the HiPerGator load was higher or if the burst qos was actively used the main qos would be more appropriate for a smaller job.
-<source lang=bash>
-$ module load ufrc
-$ slurm_info ufgi
-  Allocation summary for 'ufgi' account:
-QOS     Time Limit      Allocations (cpus, mem(MB),GPU,MIC)
-ufgi    31-00:00:00     cpu=100,mem=307200,gpu=0,mic=0
-ufgi-b  4-00:00:00      cpu=900,mem=2764800,gpu=0,mic=0
-  Current use:
-    Main QOS ('ufgi'):
-% or 81 out of 100 cores.
-% or 96GB out of 300GB memory limit.
-    Burst QOS ('ufgi-b'):
-        CPU Cores: None
-        Memory: None
-  Total HiPerGator usage:
-% or 23728 out of 31080 cores
-</source>
-=Examples=
-A hypothetical group ($GROUP in the examples below) has an investment of 42 NCUs. That's the group's so-called ''soft limit'' for HiPerGator jobs in the main qos for up to 744 hours at high priority. The hard limit accessible through the so-called ''burst qos'' is +9 times that giving a group potentially a total of 10x the invested resources i.e. 420 NCUs with burst qos providing 378 NCUs of that capacity for up to 96 hours at low priority.
-Let's test:
-<source lang=bash>
-[marvin@gator ~]$ srun --mem=126gb --pty bash -i
-srun: job 123456 queued and waiting for resources
-#Looks good, let's terminate the request with Ctrl+C>
-^C
-srun: Job allocation 123456 has been revoked
-srun: Force Terminated job 123456
-</source>
-On the other hand, going even 1gb over that limit results in the already encountered job limit error
-<source lang=bash>
-[marvin@gator ~]$ srun --mem=127gb --pty bash -i
-srun: error: Unable to allocate resources: Job violates accounting/QOS policy (job submit limit, user's size and/or time limits
-</source>
-At this point the group can try using the 'burst' QOS with
-<source lang=bash>
-#SBATCH --qos=$GROUP-b
-</source>
-Let's test:
-<source lang=bash>
-[marvin@gator3 ~]$ srun -p bigmem --mem=400gb --time=96:00:00 --qos=$GROUP-b --pty bash -i
-srun: job  123457 queued and waiting for resources
-#Looks good, let's terminate with Ctrl+C
-^C
-srun: Job allocation 123457 has been revoked
-srun: Force Terminated job 123457
-</source>
-However, now there's the burst qos time limit to consider.
-<source lang=bash>
-[marvin@gator ~]$ srun --mem=400gb --time=300:00:00 --pty bash -i
-srun: error: Unable to allocate resources: Job violates accounting/QOS policy (job submit limit, user's size and/or time limits
-</source>
-Let's reduce the time limit to what burst qos supports and try again.
-<source lang=bash>
-[marvin@gator ~]$ srun --mem=400gb --time=96:00:00 --pty bash -i
-srun: job  123458 queued and waiting for resources
-#Looks good, let's terminate with Ctrl+C
-^C
-srun: Job allocation 123458 has been revoked
-srun: Force Terminated job
-</source>
-=Pending Job Reasons=
-The following ''Reasons'' can be seen in the '<code>NODELIST(REASON)</code>' column of the ''squeue'' command when the group reaches the resource limit for the respective account/qos combination:
-==QOSGrpCpuLimit==
-All CPU cores available for the listed account within the respective QOS are in use.
-==QOSGrpMemLimit==
-All memory available for the listed account within the respective QOS as described in the previous section is in use.

Difference between revisions of "NCU and QOS limits under SLURM"

Latest revision as of 22:17, 2 November 2016

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