The Expansion Factor

  • The primary measure provided to the HPCMP user for gauging job-turnaround time is the expansion factor (EF).
  • The EF is calculated from two known properties of a job, its queue wait time (QWT) and its wall clock time (WCT).
    • EF = (QWT + WCT) / WCT
    • The minium value of the EF is one; this occurs when the QWT is zero.
  • The HPCMP establishes target levels for EFs by job class as shown in the table below.
    QueueTarget EFAcceptable QWT
    urgent 1.1 10% of WCT
    debug 1.5 50% of WCT
    high 1.6 60% of WCT
    challenge 1.7 70% of WCT
    standard 2.2 120% of WCT
    background NA NA
  • Visual Queue uses the target EFs of the queues to determine the acceptable QWT of jobs.
    • QWT = (target EF - 1)*WCT
    • Example: A challenge job requested to run for 100 hours. Thus, the acceptable amount of time that it can wait in queue is 70 hours.
  • Visual Queue colors queued jobs by the ratio of actual QWT to acceptable QWT.

Why Queued Jobs May Exceed the Target Expansion Factor

There are many reasons that a job may wait in queue longer than the acceptable wait time established by the queue's target EF. Some of these reasons are outlined below.
  • A job made a specific request and must wait for it to become available/true. These requests include but are not limited to the following:
    • Software licenses
    • Large memory nodes
    • Job dependencies
  • A job requested a large number of processors and a small wall clock time (e.g., 250 CPUs for 1 hour).
  • The job is not a good backfill candidate and must wait for a reservation.
    • The job requested a large number of processors.
    • The job requested a very long wall clock time.
  • The queues were substantially full when the job was submitted.