# K4.1 Basic principles of Job Scheduling

This skill provides an overview of the scheduling of jobs on a supercomputer.
It covers generic and widely used concepts that serve the purpose to maximize the efficiency of a supercomputer.

Batch jobs submitted to a job queue define the workloads in batch systems.
A workload manager of a cluster system typically deals with:
    * Job Control to provide a user interface for submitting jobs to job queues, monitoring their state during processing (e.g. to check their estimated starting time), and intervening in their execution (e.g. to abort them manually)
    * Scheduling and Resource Management to select a waiting job for execution and to allocate nodes to the job meeting all its other demands for computing resources (memory, special processing elements like GPUs, etc.)
    * Accounting to record historical data about how many computing resources (e.g. computing time) have been consumed by a job

## Learning Outcomes

* Comprehend the exclusive and shared usage model in HPC.
* Differentiate batch and interactive job submission.
* Comprehend the generic concepts and architecture of resource manager, scheduler, job and job script.
* Explain environment variables as a means to communicate.
* Comprehend accounting principles.
* Explain the generic steps to run and monitor a single job.
* Comprehend scheduling principles (first come first served, shortest job first, backfilling) to achieve objectives like minimizing the averaged elapsed program runtimes, and maximizing the utilization of the available HPC resources.
* Comprehend the differences between **Batch Systems** and **Time-Sharing Systems**.
* Explain the concepts and procedures for resource allocation and job execution in an HPC environment.
* Run interactive jobs and batch jobs.
* Comprehend and describe the expected behavior of job scripts.
* Change provided job scripts and embed them into shell scripts to run a variety of parallel applications.
* Analyze the output generated from a job scheduler and describe the cause of typically generated errors.
* Comprehend accounting principles (billing for the jobs).
* Comprehend the set of terms for performance criteria like:
    * Resource Utilization.
    * Throughput.
    * Waiting Time.
    * Execution Time.
    * Turnaround Time.
* Comprehend scheduling strategies that increase productivity.
* Comprehend that typical goals of job scheduling are:
    * Maximization of resource utilization.
    * Maximization of throughput.
    * Minimization of waiting time.
    * Minimization of turnaround time.
* Comprehend that there is a variety of scheduling algorithms from rather simple to more complex like:
    * First-Come-First-Served (FCFS).
    * Shortest-Job-First (SJF).
    * Priority-based.
    * Fair-Share.
    * Backfilling.
* Apply advanced scheduling principles (e.g. backfilling) to achieve objectives like minimizing the averaged elapsed program runtimes, and maximizing the utilization of the available HPC resources.
* Discuss sophisticated scheduling principles (e.g. fair share) to achieve objectives like treating the users fair, and maximizing the utilization of the available HPC resources.