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.
  

  Queue	Target EF	Acceptable 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.