CPU: Hyperthreading ON/OFF (HT ON/OFF)

Hyperthreading is a new feature supported in HP-UX 11i v3 (11.31) environments on servers with the dual core Intel Itanium processors. It provides for executing multiple threads on a single core. This allows multiple hardware threads to share under-utilized resources, increasing overall throughput and performance. Throughput increases are typically achieved by making use of the idle cycles and idle functional units that occur due to memory stalls. For more information on hyperthreading and performance, see the white paper Dynamic Logical Processors for Hyper-Threading on HP-UX 11i v3 available at http://docs.hp.com.

Hyperthreading is supported within vPars A.05.xx environments. However, note the following details.

HT ON/OFF can be set using any of the following commands.

The vPar Monitor’s threads command.

The syntax is:

threads [on|off]

For example:

MON> threads
HyperThreading is currently OFF
HyperThreading will be OFF after the next nPar reboot
MON> threads on
HyperThreading is now set to be ON after the next reboot
MON> threads
HyperThreading is currently OFF
HyperThreading will be ON after the next nPar reboot
MON> threads off
HyperThreading is now set to be OFF after the next reboot

The EFI shell’s cpuconfig command.
The syntax is:
cpuconfig threads [on|off]
For a primer on cpuconfig, see “Setting Hyperthreading (HT ON/OFF) and cpuconfig Primer”.
The HP-UX shell’s parmodify command.
The syntax is:
parmodify -T y|n
The HP-UX shell’s setboot command.
The syntax is:
setboot -m on|off

For more information on using or setting HT ON/OFF, see the nPartition Administrator's Guide.

Although hyperthreading is supported within vPars, CPU assignments to virtual partitions remain on a per-core basis and not on a logical CPU (LCPU) basis.
This means that all the vPars commands for CPUs work the same as they did in vPars A.04.xx, including using the same legacy hardware path format.
HT ON is not supported in a mixed HP-UX 11i v2/v3 vPars environment or mixed HP-UX 11i v1/v2/v3 vPars environment.
Turning hyperthreading on or off at the EFI level or vPars Monitor level has nPar wide scope. Individual virtual partitions can use the HP-UX command lcpu_attr to turn logical processors on or off within processor sets in a virtual partition. However, if hyperthreading is turned off at the EFI or vPars Monitor level, the lcpu_attr command will not have any effect.

CPU: Hyperthreading ON/OFF (HT ON/OFF)

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