Managing Kernel Tunable Parameters with HP SMH

HP SMH can be used to query and change the values of kernel tunable parameters (“tunables”) in the currently running configuration. Using HP SMH, you can:

Modify the value of a tunable
View details about a tunable
Search for a tunable
Check the current and next boot value for a tunable
Print details about a tunable or print a list of all tunables

You can view the tunables pane by selecting the Tunables tab on the HP SMH Kernel Configuration page, as shown in Figure 10-5.

Figure 10-5 Kernel Configuration Tunables Tab

Getting Information About Tunables

To get more detailed information about a particular tunable, do the following:

Scroll to the tunable in the list.
Click the radio button.

The tunable details are displayed under the list, as shown in Figure 10-6.

Figure 10-6 Kernel Configuration Tunable Details

Interpreting Tunable Information

The tunable details block and the tunable list contain the information shown in Table 10-5.

Table 10-5 Tunable Details Fields

Field Name	Description
Tunable	The name of the tunable.
Description	A brief description of the tunable.
Module	The name of the module (if any) that the tunable is associated with.
Tuning Capability	Whether the tunable is `Static`, `Dynamic`, or `Auto`.
Default	The default value for the tunable.
Current Value	The current maximum value for the resource.
Next Boot Value	The planned value, with all formulae computed.
Next Boot Value (Expression)	The formula (or integer) describing the next boot value.
Range	The range of values that are valid for the tunable.
Constraints	The dependencies that a tunable might have on other tunables as well as value restrictions.
Current Usage	The percentage of the resource that is being used.

Changing Tunable Values

To change the value of a tunable, execute the following steps:

Select the tunable.

Click Modify Tunable in the right-hand column of the window.

The Modify Kernel Tunable page is displayed, as shown in Figure 10-7.

Figure 10-7 Modify Kernel Tunable

The Modify Kernel Tunable page displays the fields shown in Table 10-6.

Table 10-6 Modify Kernel Tunable Fields

Field Name	Description
Tunable Name	The name of the tunable that will be modified.
Description	Description of the tunable.
Module	The kernel module that the tunable is associated with.
Default	The default value of the tunable.
Range	The range of acceptable values for the tunable. Negative numbers are indicated by a minus sign (`-`). Positive numbers are unsigned. `Not Available` indicates that the underlying command, kctune, is returning neither a minimum nor a maximum value.
Current Value	The current value of the tunable.
Tuning Capability	Displays whether the tunable is `Static`, `Dynamic`, or `Auto`.
Current Usage	The percentage of the resource that is being used.
Constraints	The dependencies that a tunable might have on other tunables and its value restrictions

The Modify Kernel Tunable page also displays the areas that you can change, as shown in Table 10-7. The areas displayed depend on the capabilities of the tunable. Enter your changes.

Table 10-7 Modify Kernel Tunable Change Options

Field Name	Description
New Setting (Expression/Value)	Enter a formula (or integer) describing the new value. You can set it to the default by clicking the Reset to Default button.
New Setting (Evaluated)	The calculated value of the new setting. You may have to click the Recalculate Value button.
Mode of Change	Select either change immediately or change at next boot. The default is change at next boot. This field only appears for dynamic tunables. Other tunables always change at next boot.
Backup	Check whether to back up the current configuration before applying the change. By default, this check box is selected.
Reason for Change	Enter comments about the change in the tunable value.

(Optional) To see the command that will execute the changes, click the Preview button.
After you have entered your changes, click the Modify button to execute them. Or click the Cancel button to discard your changes.

Managing Kernel Tunable Parameters with HP SMH

Technical documentation

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Getting Information About Tunables

Interpreting Tunable Information

Changing Tunable Values