HP OpenVMS Systems Documentation

Content starts here B.4 Enabling or Disabling Hyper-Threading on Dual-Core Processors
HP OpenVMS Version 8.4 Upgrade and Installation Manual > Appendix B Configuring OpenVMS Integrity servers Hardware Operation and Boot Operations, and Booting and Shutting Down Your System

B.4 Enabling or Disabling Hyper-Threading on Dual-Core Processors

Systems that have Intel Itanium Dual-Core processors can support Hyper-Threading. Hyper-Threading provides the ability for processors to create an additional logical CPU that might allow additional efficiencies of processing. For example, a dual-core processor with Hyper-Threading active provides four logical CPUs, two on each core. The effect that Hyper-Threading has on performance depends heavily on the applications running on your system. HP recommends that you start with Hyper-Threading disabled and experiment later, if you wish.

You can enable or disable Hyper-Threading for a system whose processors support it. To display the Hyper-Threading state for a system, use the EFI info cpu or cpuconfig command. (The display indicates that “CPU threads” are turned on or off.) For example:

Shell> cpuconfig

        # of               L3      L4      Family/
CPU     Logical            Cache   Cache     Model          Processor
Module     CPUs   Speed    Size    Size     (hex.)    Rev   State
-----   -------   ------   ------  ------  ---------  ---   -----
 0           4    1.4 GHz   6 MB   None    20/00      CO    Active

CPU threads are turned on.

To enable or disable Hyper-Threading, use the EFI cpuconfig threads on or cpuconfig threads off command. For more information, enter help cpuconfig at the EFI Shell prompt or see the appropriate hardware documentation. The recent release of the Partition Manager also supports Hyper-Threading.

After enabling or disabling Hyper-Threading, the system must be reset for the change to take effect. Use the EFI Shell reset command. When Hyper-Threading is enabled, it remains active on the next reboot of the system.