HP Process Resource Manager User's Guide

Understanding how PRM manages resources
How PRM manages CPU resources
Chapter 2 47
CPU allocation and number of shares assigned
When managing FSS PRM groups, PRM favors processes in groups with
a larger number of CPU shares over processes in groups with fewer CPU
shares. Processes in FSS PRM groups with a larger number of CPU
shares are scheduled to run more often and are given more opportunities
to consume CPU time than processes in other FSS PRM groups. This
preference implies that the process in an FSS PRM group with a larger
number of shares may have better response times with PRM than with
the standard HP-UX scheduler.
An FSS PRM group can use more than its configured CPU allocation
when the system is at nonpeak load—unless CPUCAPON mode is enabled
or a per-group cap equal to its allocation has been assigned. (For more
information on capping options, see the next section, “Capping CPU
resource use”.)
Capping CPU resource use
PRM gives you two options for capping CPU resource use by FSS PRM
groups:
• On a per-group basis
(Available for HP-UX 11i v3 and later.) For per-group capping, use
the MAX field in the FSS PRM group record (discussed in the section
“Group/CPU record syntax” on page 105) for only those groups you
want to cap.
• For all FSS PRM groups in the configuration
The CPUCAPON mode, enabled through the prmconfig -M option
discussed below, treats the FSS PRM group’s minimum allocation as
its maximum allocation.
When CPUCAPON mode is enabled, CPU capping is in effect for all
user-configured FSS PRM groups on a system—regardless of CPU
load. Each FSS PRM group takes its entire CPU allocation. Thus, no
group can obtain more CPU resources.
The PRM_SYS group, however, is exempt from capping. If it gets CPU
time and has no work, the PRM scheduler immediately goes to the
next FSS PRM group.