HP Process Resource Manager User's Guide

Understanding how PRM manages resources
How PRM manages CPU resources
Chapter 2 43
• Enables making higher-level policy decisions—By placing groups in a
hierarchy, you can implement changes in policy or funding at a
higher level in a configuration without affecting all elements of the
configuration.
• Facilitates system upgrades, capacity planning, and partitioning—If
you are moving from a two-core system to a four-core system, you can
reserve the two additional cores by adding a place-holder group at
the top level in the hierarchy, assigning it shares equal to 50% of the
CPU resources, and enabling capping. This place-holder prevents
users from getting a boost in performance from the new cores, then
being frustrated by poor performance when more applications are
added to the system.
The syntax for hierarchical groups is explained in “Group/CPU record
syntax” on page 105.
By default, PRM utilities (prmconfig, prmlist, prmmonitor) include
only leaf groups in their output. Use the -h option to display information
for parent groups as well.
How PRM manages CPU resources
This section describes how PRM manages CPU resources. To understand
PRM’s CPU management, it is useful to know how the standard HP-UX
scheduler works.
The HP-UX scheduler chooses which process to run based on priority.
Except for real-time processes, the system dynamically adjusts the
priority of a process based on resource requirements and resources used.
In general, when processes are not running, the HP-UX scheduler raises
their priorities; and while they are running, their priorities are lowered.
The rate at which priority declines during execution is linear. The rate at
which priority increases while waiting is exponential, with the rate of
increase fastest when the CPU load is low and slowest when the CPU
load is high. When a process other than the current process attains a
higher priority, the scheduler suspends the current process and starts
running the higher priority process.