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lcpu_attr(5)							  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  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 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)

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