HP Process Resource Manager User's Guide

Understanding how PRM manages resources

How PRM controls resources

Chapter 234

PRM groups

PRM groups are integral to how PRM works. These groups are assigned

per process and are independent of any other groups, such as user groups

that are deﬁned in /etc/group. You assign applications and users to PRM

groups. PRM then manages each group’s CPU, disk bandwidth, and real

memory resources (private and shared) according to the current

conﬁguration. If multiple users or applications within a PRM group are

competing for resources, standard HP-UX resource management

determines the resource allocation.

There are two types of PRM groups:

FSS PRM groups are the traditional and most commonly used PRM

group. These groups have CPU, private memory, and disk bandwidth

resources allocated to them using the shares model. (Shared memory is

speciﬁed in megabytes.) FSS PRM groups use the Fair Share Scheduler

in the HP-UX kernel within the system’s default processor set (PSET).

PSET PRM groups are the second type of PRM group. In PSET PRM

groups, the CPU entitlement is speciﬁed by assigning them a subset of

the system’s cores—instead of using the shares model. (A core is the

actual data-processing engine within a processor. A single processor

might have multiple cores. A core might support multiple execution

threads, as explained in the section “Hyper-Threading” on page 49.) The

private memory allocation is still speciﬁed in shares and shared memory

is still in megabytes; however, the PSET PRM groups are treated as part

of PRM_SYS (PRMID 0) for disk bandwidth purposes. Processes in a PSET

PRM group have equal access to CPU cycles through the HP-UX

time-share scheduler.

Because resource management is performed on a group level, individual

users or applications may not get the resources required in a group

consisting of many users or applications. In such cases, reduce the

number of users and applications in the group or create a group

speciﬁcally for the resource-intensive user or application.

Resource allocation

Resources are allocated to PRM groups differently depending on the

resource and the type of PRM group. For FSS PRM groups, resources are

typically allocated in shares. For PSET PRM groups, you allocate CPU