lcpu_attr(5)lcpu_attr(5)NAMElcpu_attr - dynamically enable or disable LCPU attribute of the default
processor set
VALUES
Fail Safe
Default
the LCPU attribute of the default processor set is disabled
Allowed values
or
DESCRIPTION
This tunable dynamically enables or disables 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 dis‐
abled, 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 advantage 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 parame‐
ter 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 val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
AUTHOR
was developed by HP.
SEE ALSOpsrset(1M), pset_assign(2), pset_bind(2), pset_create(2), pset_ctl(2),
pset_destroy(2), privgrp(4).
Tunable Kernel Parameters lcpu_attr(5)