HP-UX Workload Manager User's Guide

Introduction
Why use Workload Manager?
Chapter 1 49
• Optional conditions, such as time of day or a particular event
• Optional lower and/or upper bounds for CPU resources
A shares-based SLO consists of the same elements except it does not
include a goal but rather a shares allocation.
For more information comparing shares-based and goal-based SLOs, see
“Shares-based SLOs vs goal-based SLOs” on page 118.
Prioritized SLOs
Another important reason for using WLM is that it allows you to
prioritize the SLOs. When CPU resources are not sufficient to satisfy all
SLOs, WLM grants CPU resources to the highest priority SLOs first.
After the demands of the higher priority SLOs are satisfied, WLM grants
the lower priority SLOs any resources that remain available. Valid
priorities start at 1, with 1 being the highest priority.
SLO priorities do not have to be uniquely assigned—multiple SLOs can
be granted the same priority, allowing more than one workload’s
objective to be top priority. This can be beneficial when multiple
workloads are equally important. Typically, all the SLOs in a given
configuration should not be assigned the same priority; otherwise, under
a heavy system load, WLM may not be able to allocate CPU resources
effectively when there is not enough resources to satisfy all SLOs.
A single workload can have multiple SLOs, each with a different priority.
One SLO would be the high priority, “must meet” goal and the remaining
SLOs would be lower priority, “meet if possible” goals. For example, a
priority 1 goal might be associated with a virtual partition to maintain
an allocation of at least two cores. A priority 2 goal might be to allocate
three or four cores if available when the workload becomes very busy.
This lower priority goal (a “stretch goal”) is met only after the priority 1
SLOs for this workload and all other workloads are met.
For information on how WLM uses priorities, see “Allocating CPU
resources: The rising tide model” on page 122.