Basic configuration file for CPU control

Red Hat Enterprise Linux 9.2 LPAR mode z/VM guest KVM guest

A configuration file for dynamically enabling or disabling CPUs has several required specifications.

The configuration file sample of Figure 1 has been reduced to the specifications that are required for dynamically enabling or disabling CPUs.

Figure 1. Simplified configuration file with CPU hotplug rules

UPDATE="10"
CPU_MIN="2"
CPU_MAX="10"

HOTPLUG = "idle < 10.0"
HOTUNPLUG = "idle > 100"

In the configuration file:

UPDATE

specifies the time interval, in seconds, at which cpuplugd evaluates the rules and, if a rule is met, enables or disables CPUs. This variable is also required for controlling memory (see Basic configuration file for memory control).

In the example, the rules are evaluated every 10 seconds.

CPU_MIN

specifies the minimum number of CPUs. Even if the rule for disabling CPUs is met, cpuplugd does not reduce the number of CPUs to less than this number.

In the example, the number of CPUs cannot become less than 2.

CPU_MAX

specifies the maximum number of CPUs. Even if the rule for enabling CPUs is met, cpuplugd does not increase the number of CPUs to more than this number. If 0 is specified, the maximum number of CPUs is the number of CPUs available on the system.

In the example, the number of CPUs cannot become more than 10.

HOTPLUG

specifies the rule for dynamically enabling CPUs. The rule resolves to a boolean true or false. Each time this rule is true, cpuplugd enables one CPU, unless the number of CPUs has already reached the maximum specified with CPU_MAX.

Setting HOTPLUG to 0 disables dynamically adding CPUs.

In the example, a CPU is enabled when the idle times of all active CPUs sum up to less than 10.0%. See Keywords for CPU hotplug rules for information about available keywords.

HOTUNPLUG

specifies the rule for dynamically disabling CPUs. The rule resolves to a boolean true or false. Each time this rule is true, cpuplugd disables one CPU, unless the number of CPUs has already reached the minimum specified with CPU_MIN.

Setting HOTUNPLUG to 0 disables dynamically removing CPUs.

In the example, a CPU is disabled when the idle times of all active CPUs sum up to more than 100%. See Keywords for CPU hotplug rules for information about available keywords.

If one of these variables is set more than once, only the last occurrence is used. These variables are not case sensitive.

If both the HOTPLUG and HOTUNPLUG rule are met simultaneously, HOTUNPLUG is ignored.