lcpu_attr(5) File Formats Manual lcpu_attr(5)
NAME
lcpu_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
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 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 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 tun-
able values, 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 ALSO
psrset(1M), pset_assign(2), pset_bind(2), pset_create(2), pset_ctl(2), pset_destroy(2), privgrp(4).
Tunable Kernel Parameters lcpu_attr(5)