dynamically tunable kernel parameters in hp-ux 11i 1 july 2000 an hp-ux 11i white paper from Hewlett-Packard
table of contents abstract 3 introduction 3 what are tunables? 3 what is changing? 3 which tunables are dynamic? 4 changing tunable values changing tunable parameters with SAM 4 changing tunable parameters with kmtune and mk_kernel 5 using dynamic tunable APIs 5 persistence of kernel tuning 5 persistence across reboots 6 persistence across kernel rebuilds 6 kernel rebuilds take precedence 6 documentation 2 4 6 documentation on tuning in general 6 documentation on specific tuna
dynamically tunable kernel parameters in hp-ux 11i abstract This white paper discusses dynamically tunable or configurable kernel parameters (known as “tunables”) in HP-UX 11i, and the mechanisms that are available to manage them. The paper explains tunable parameters, illustrates how to determine which parameters are dynamic, and discusses the ways to change those parameters. The paper also includes an explanation of the persistence of changed parameters.
which tunables are dynamic? A tunable may be either static, dynamic, or automatic: • A static tunable is one whose value cannot be changed without rebooting the system. Usually a kernel rebuild is also required. • A dynamic tunable is one whose value can be changed without a reboot. • An automatic tunable is one that is constantly being tuned by the kernel itself, in response to changing system conditions.
Figure 2: Determining whether a tunable parameter can be changed without rebooting Information about each tunable can be found in the online help system for SAM. This data is also available on docs.hp.com. (Go to your current HP-UX release and then search for “Configurable Kernel Parameters.”) changing tunable parameters with kmtune and mk_kernel The kmtune(1M) command is HP-UX’s supported method for changing the values of tunable parameters from the command line.
persistence across reboots All tunable value changes made through any method will remain persistent when the kernel reboots, as long as it is neither rebuilt nor renamed. Tunable values are stored in the Kernel Registry Service (KRS), a persistent storage mechanism. Every time the system boots, it retrieves the stored values of tunables from KRS and uses them. As a result, tunable value changes will persist across reboots.
troubleshooting Even with the best of intentions, it is possible to make a tunable value change that degrades system performance. Such degradations may be immediately apparent, or they may take some time to become noticeable. It is critically important that records be kept of all tunable value changes, so that they can be reversed if needed. Dynamic tunable changes are automatically recorded to syslog and to the Kernel Logging subsystem.
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