7.3 Quality of Service (QoS) Facilities
This section describes how to do the following:
Moab's QoS facility allows a site to give special treatment to various classes of jobs, users, groups, and so forth. Each QoS object can be thought of as a container of special privileges ranging from fairness policy exemptions, to special job prioritization, to special functionality access. Each QoS object also has an extensive access list of users, groups, and accounts that can access these privileges.
Sites can configure various QoS's each with its own set of priorities, policy exemptions, and special resource access settings. They can then configure user, group, account, and class access to these QoS's. A given job will have a default QoS and may have access to several additional QoS's. When the job is submitted, the submitter may request a specific QoS or just allow the default QoS to be used. Once a job is submitted, a user may adjust the QoS of the job at any time using the setqos command. The setqos command will only allow the user to modify the QoS of that user's jobs and only change the QoS to a QoS that this user has access to. Moab administrators may change the QOS of any job to any value.
Jobs can be granted access to QoS privileges if the QoS is listed in the system default configuration QDEF (QoS default) or QLIST (QoS access list), or if the QoS is specified in the QDEF or QLIST of a user, group, account, or class associated with that job. Alternatively, a user may access QoS privileges if that user is listed in the QoS's MEMBERULIST attribute.
The mdiag -q command can be used to obtain information about the current QoS configuration including specified credential access.
The privileges enabled via QoS settings may be broken into the following categories:
All privileges are managed via the QOSCFG parameter.
# assign priority for all qos geo jobs QOSCFG[geo] PRIORITY=10000
The QoS facility can be used to enable special services and to disable default services. These services are enabled/disabled by setting the QoS QFLAGS attribute.
Example: For lowprio QoS job, disable backfill and make job preemptible
Example: Bind all jobs to chemistry reservation
Other QoS Attributes
In addition to the flags, there are attributes that alter service access.
Example: All jobs submitted under a QoS sample receive a system priority of 1
Per QoS Required Reservations
If desired, jobs associated with a particular QoS can be locked into a reservation or reservation group using the REQRID attribute. For example, to force jobs using QoS jasper to only use the resources within the failsafe standing reservation, use the following:
QOSCFG[jasper] REQRID=failsafe ...
Minimum network service levels can be specified using the MINBANDWIDTH and MAXLATENCY attributes. If specified, Moab does not allow a job to start until these criteria can be satisfied and allocates or reserves specific resources or combinations of resources to fulfill these constraints. Further, if the Network Management System supports it, Moab dynamically creates network fabric partitions with guaranteed service levels.
QOSCFG[highspeed] MINBANDWIDTH=1GB MAXLATENCY=10us ...
All credentials, including QoS, allow specification of job usage limits as described in the Basic Fairness Policies overview. In such cases, jobs are constrained by the most limiting of all applicable policies. With QoS's, an override limit may also be specified and with this limit, jobs are constrained by the override, regardless of other limits specified. In particular, the following policies may be overridden:
Usage limits are overridden by specifying the QoS attribute O<LIMIT>, as in OMAXJOB or OMAXPROC. To override system/job limits, use the OMAXJ<LIMIT>, as in OMAXJPS or OMAXJWC.
In addition to job usage limits, QoS's (as with other credentials), can also limit personal reservations. Attributes such as RMAXDURATION, RMAXPROC, and RMAXTOTALPROC can be used to constrain resources available to personal reservations. See Personal Reservation Usage Limits for more information.
# staff QoS should have a limit of 48 jobs, ignoring the user limit USERCFG[DEFAULT] MAXJOB=10 QOSCFG[staff] OMAXJOB=48
Jobs can be granted access to services such as preemption and reservation creation, and they can be granted access to resource reservations. However, with QoS thresholds, this access can be made conditional on the current queuetime and XFactor metrics of an idle job. The following table lists the available QoS service thresholds:
Job preemption facilities can be controlled on a per-QoS basis using the PREEMPTEE and PREEMPTOR flags. Jobs that are preemptible can optionally be constrained to only be preempted in a particular manner by specifying the QoS PREEMPTPOLICY attribute as in the following example:
QOSCFG[special] QFLAGS=PREEMPTEE PREEMPTPOLICY=CHECKPOINT
For preemption to be effective, a job must be marked as a preemptee and must be enabled for the requested preemption type. For example, if the PREEMPTIONPOLICY is set to suspend, a potential target job must be both a preemptee and marked with the job flag SUSPENDABLE. (See suspension for more information.) If the target job is not suspendable, it will be either requeued or canceled. Likewise, if the PREEMPTIONPOLICY is set to requeue, the job will be requeued if it is marked restartable. Otherwise, it will be canceled.
The minimum time a job must run before being considered eligible for preemption can also be configured on a per-QoS basis using the PREEMPTMINTIME parameter, which is analogous to the JOBPREEMPTMINACTIVETIME. Conversely, PREEMPTMAXTIME sets a threshold for which a job is no longer eligible for preemption; see JOBPREEMPTMAXACTIVETIME for analogous details.
Specifying Credential Based QoS Access
You can define the privileges allowed within a QoS by using the QOSCFG parameter; however, in most cases access to the QoS is enabled via credential specific *CFG parameters, specifically the USERCFG, GROUPCFG, ACCOUNTCFG, and CLASSCFG parameters, which allow defining QoS access lists and QoS defaults. Specify credential specific QoS access by using the QLIST and/or QDEF attributes of the associated credential parameter.
QOS Access via Logical OR
To enable QoS access, the QLIST and/or QDEF attributes of the appropriate user, group, account, or class/queue should be specified as in the following example:
# user john's jobs can access QOS geo, chem, or staff with geo as default USERCFG[john] QDEF=geo QLIST=geo,chem,staff # group system jobs can access the development qos GROUPCFG[systems] QDEF=development # class batch jobs can access the normal qos CLASSCFG[batch] QDEF=normal
By default, jobs may request a QoS if access to that QoS is allowed by any of the job's credentials. (In the previous example, a job from user john submitted to the class batch could request QoS's geo, chem, staff, or normal).
QOS Access via Logical AND
If desired, QoS access can be masked or logically ANDed if the QoS access list is specified with a terminating ampersand (&) as in the following example:
# user john's jobs can access QOS geo, chem, or staff with geo as default USERCFG[john] QDEF=geo QLIST=geo,chem,staff # group system jobs can access the development qos GROUPCFG[systems] QDEF=development # class batch jobs can access the normal qos CLASSCFG[batch] QDEF=normal # class debug jobs can only access the development or lowpri QoS's regardless of other credentials CLASSCFG[debug] QLIST=development,lowpri&
QoS access may also be specified from within the QoS object using the QoS MEMBERULIST attribute as in the following example:
Charging policies and rates may be configured on a per-QoS basis. This capability provides a powerful way of allowing end-users to select the level of service they desire and the price they are willing to pay for that service.
Several policies allow control over exactly how a job gets charged; these include CHARGERATEPOLICY and CHARGEMETRICPOLICY. The first parameter, CHARGERATEPOLICY, allows a site to specify how jobs are charged for the resources they use.
A job's total cost can be adjusted on a per QoS basis using the DEDRESCOST attribute:
QOSCFG[fast] DEDRESCOST=4.0 QOSCFG[slow] DEDRESCOST=0.5 ...
By default, jobs inherit a default QoS based on the user, group, class, and account associated with the job. If a job has access to multiple QoS levels, the submittor can explicitly request a particular QoS using the QoS resource manager extension as in the following example:
> msub -l nodes=1,walltime=100,qos=special3 job.cmd
By default, Moab allows all users access to special attributes such as node access policy. By enabling the QoS facility SPECATTRS, the access to these policies can be restricted. For example, to enable the facility, in the moab.cfg file, specify QOSCFG[DEFAULT] SPECATTRS=. Then, to allow access to the special attributes, indicate which special attributes a specific QoS may access.
QOSCFG[DEFAULT] SPECATTRS= QOSCFG[high] SPECATTRS=NACCESSPOLICY
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