Tunable Kernel Parameters
NAME [Toc] [Back]
dnlc_hash_locks - number of locks for the Directory Name Lookup Cache
VALUES [Toc] [Back]
Default [Toc] [Back]
Allowed values [Toc] [Back]
The minimum value allowed is 16. The maximum value allowed is 8192.
The value is further constrained in that it must be be a power of 2,
and it must be equal to or less than one eighth the number of DNLC
entries (ncsize >= 8 * dnlc_hash_locks).
Specify a positive integer value.
DESCRIPTION [Toc] [Back]
To speed up the search through directories in the kernel, there is a
memory resident cache of directories called the Directory Name Lookup
Cache (DNLC). During a filename lookup in the kernel, any directories
or files encountered are retained in the DNLC for future reference.
The DLNC is managed in a Least Recently Used (LRU) fashion. The
dnlc_hash_locks dictates the number of lock groups that will be used
to manage the directory entries in the DNLC hash chains.
Who Is Expected to Change This Tunable?
HP-UX system administrators.
Restrictions on Changing [Toc] [Back]
This tunable is static. Any changes to the value of this tunable will
require system reboot before taking effect.
When Should the Value of This Tunable Be Raised?
The value may need to be raised to reduce lock contention and improve
filename lookup performance when running applications which require
large numbers of filename access.
What are the Side Effects of Raising the Value?
More system memory will be consumed to allocate locks for the DNLC.
When Should the Value of This Tunable Be Lowered?
The value can be lowered to limit the number of locks allocated for
the DNLC and reduce memory consumption.
What are the Side Effects of Lowering the Value?
Less system memory will be consumed for the DNLC locks upon system
reboot. Operations requiring filename lookup (e.g. open(2)) may
experience performance degradation.
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
Tunable Kernel Parameters
What Other Tunable Values Should Be Changed at the Same Time?
The value of ncsize must be equal to or greater than eight times the
value of dnlc_hash_locks (ncsize >= 8 * dnlc_hash_locks).
WARNINGS [Toc] [Back]
All HP-UX kernel tunable parameters are release specific. This
parameter may be removed or have its meaning changed in future
releases of HP-UX.
Installation of optional kernel software, from HP or other vendors,
may cause changes to tunable parameter values. After installation,
some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable
values, consult the documentation for the kernel software being
installed. For information about optional kernel software that was
factory installed on your system, see HP-UX Release Notes at
AUTHOR [Toc] [Back]
dnlc_hash_locks was developed by HP.
SEE ALSO [Toc] [Back]
kctune(1M), sam(1M), gettune(2), settune(2), dnlc_hash_locks(5).
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]