Absolute job priority scheduling (APS) provides a mechanism to control the job dispatch order to prevent job starvation.
When configured in a queue, APS sorts pending jobs for dispatch according to a job priority value calculated based on several configurable job-related factors. Each job priority weighting factor can contain subfactors. Factors and subfactors can be independently assigned a weight.
APS only sorts the jobs; job scheduling is still based on configured LSF scheduling policies. LSF attempts to schedule and dispatch jobs based on their order in the APS queue, but the dispatch order is not guaranteed.
The job priority is calculated for pending jobs across multiple queues based on the sum of configurable factor values. Jobs are then ordered based on the calculated APS value.
To configure absolute priority scheduling (APS) across multiple queues, define APS queue groups. When you submit a job to any queue in a group, the job's dispatch priority is calculated using the formula defined in the group's master queue.
Administrators can also set a static system APS value for a job. A job with a system APS priority is guaranteed to have a higher priority than any calculated value. Jobs with higher system APS settings have priority over jobs with lower system APS settings.
Administrators can use the ADMIN factor to manually adjust the calculated APS value for individual jobs.
To calculate the job priority, APS divides job-related information into several categories. Each category becomes a factor in the calculation of the scheduling priority. You can configure the weight, limit, and grace period of each factor to get the desired job dispatch order.
LSF sums the value of each factor based on the weight of each factor.
The weight of a factor expresses the importance of the factor in the absolute scheduling priority. The factor weight is multiplied by the value of the factor to change the factor value. A positive weight increases the importance of the factor, and a negative weight decreases the importance of a factor. Undefined factors have a weight of 0, which causes the factor to be ignored in the APS calculation.
The limit of a factor sets the minimum and maximum absolute value of each weighted factor. Factor limits must be positive values.
Each factor can be configured with a grace period. The factor only counted as part of the APS value when the job has been pending for a long time and it exceeds the grace period.