HP-UX Workload Manager User's Guide

Configuring WLM

Tuning the metrics and the SLOs

Chapter 5232

WLM uses this value to re-target the goal it is trying to

converge on. For example, with a margin_value of 0.1

and a goal of X, the re-targeted goal is X - (0.1*X). The

controller adjusts the goal up or down (based on

whether the goal is > or <) by this percentage to create

a buffer zone. This adjustment prevents small

fluctuations in the service level from causing SLO

violations.

Consider Figure 5-6. Assume the goal in the

configuration file is response_time < 2 seconds, and the

default cntl_margin value of 0.1 is in effect. WLM

internally re-targets the goal to 1.8 seconds (0.1*2 =

0.2; 2 - 0.2 = 1.8). As shown, the response_time values

are close to 1.8, with some values below and some

above the re-targeted goal. Without cntl_margin,

these values would converge from below and above on

the goal in the configuration file. Each value above the

goal would then cause an SLO violation. With the

re-targeted goal, these fluctuations do not cause SLO

violations.

NOTE The “cntl_margin = margin_value” tunable applies

only to performance goals. Do not use it with usage

goals.

Figure 5-6 Effect of the cntl_margin tunable parameter

Goal

Re-targeted goal

response_time