Dynamically Tunable Parameters in HP-UX 11i

6
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.
It is important to note that KRS maintains a separate set of tunable values for
each different kernel file name. Tunable changes made after booting the kernel
/stand/vmunix will affect any future boots of /stand/vmunix, but will not affect
any boots of /stand/vmunix.other. As a result, tunable changes are not persistent
when a kernel is renamed, or when switching between two kernels with different names.
persistence
across kernel
rebuilds
The system files contain the tunable settings that are used when a kernel is built. There
is one file for the core kernel and another for each separately loadable kernel module.
SAM and kmtune(1M) automatically update these files whenever they are used to
change a tunable value. As a result, all subsequent kernel builds will incorporate the
new value of a tunable. Therefore, all tunable changes made using SAM or kmtune
will remain persistent across kernel rebuilds.
kernel rebuilds
take precedence
When a kernel gets rebuilt, the tunable data in KRS is erased and replaced with the
tunable data in the system files.
2
In most cases, this will not matter; if SAM or kmtune
is used to change tunable values, then both sources of data are kept synchronized.
However, the settune(2) API does not update the system files. Unless they are
updated separately, the changes made using settune will be lost when the kernel
is next rebuilt.
documentation
It can be difficult to determine how to set tunables to achieve best system performance.
(Indeed, no two system administrators have exactly the same definition of “best system
performance.”) HP does provide a number of resources for those who wish to learn more
about tunables. We will be concentrating, over the next few releases, on augmenting and
improving these resources.
documentation on
tuning in general
To learn more about “Managing System Performance and Steps to Reconfigure the
Kernel,” see the chapter by that name in the HP-UX manual titled Managing Systems
and Workgroups: A Guide for HP-UX System Administrators.
Web-based documentation on some common tuning situations can be found on
docs.hp.com. (Go to your current HP-UX release and then search for “Configurable
Kernel Parameters.”)
An excellent reference is the book HP-UX Tuning and Performance: Concepts, Tools,
and Methods, First Edition, by Robert Sauers. This book was published in July 1999 by
Prentice Hall PTR, ISBN 0-13-102716-6.
documentation on
specific tunables
The most up-to-date source of documentation on specific tunables is in the online help
system within SAM. This data is also available on docs.hp.com. (Go to your current
HP-UX release and then search for “Configurable Kernel Parameters.”)
2
More precisely, the erasure and replacement happens when the rebuilt kernel is first booted.