lcpu_attr.5 (2010 09)

l
lcpu_attr(5) lcpu_attr(5)
(Tunable Kernel Parameters)
NAME
lcpu_attr - dynamically enable or disable LCPU attribute of the default processor set
VALUES
Fail Safe
0 (off)
Default
0 (off) the LCPU attribute of the default processor set is disabled
Allowed values
0 (off)or1 (on
)
DESCRIPTION
This tunable dynamically enables (
1) or disables (
0) the logical processor (LCPU) attribute in the default
processor set. On systems supporting hyper-threading technology, each hyper-thread is represented as
an LCPU.
When the LCPU attribute is enabled, the processor cores in the default processor have hyper-threading
enabled. If the LCPU attribute is disabled, the physical processors in the default processor set behave as
single threaded processor cores.
See pset_setattr (2) for information about managing the LCPU attribute in processor sets other than the
default processor set.
Who Is Expected to Change This Tunable?
System administrators that wish to change hyper-threading ability in the default processor set.
Restrictions on Changing
The tunable has no effect on platforms that do not have hyper-threading capability or systems with
hyper-threading disabled at the firmware level. On systems that support hyper-threading, the firmware
feature must be enabled to dynamically enable/disable the LCPU attribute in the default processor set.
When Should the Tunable Be Turned On?
The tunable should be turned on to enable the LCPU attribute in the default processor set to take advan-
tage of hyper-threading. If the applications running on the system see performance benefits, the LCPU
attribute should remain enabled.
What Are the Side Effects of Turning the Tunable On?
Some workloads may experience performance degradation when the LCPU attribute is enabled.
When Should the Tunable Be Turned Off?
Some applications may experience performance degradation or may not see any performance benefits
from using hyper-threading. In this case, this tunable should be turned off.
What Are the Side Effects of Turning the Tunable Off?
With LCPU turned off, applications may not take advantage of hyper-threading.
What Other Tunables Should Be Changed at the Same Time?
None.
WARNINGS
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 parame-
ter 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
http://www.hp.com/go/hpux-core-docs.
AUTHOR
lcpu_attr was developed by HP.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1