hyperthread(HW)

hyperthread -- enable two logical processors per physical CPU

Description

Hyper-Threading (HT) Technology allows two series of instructions to run simultaneously and independently on a single Intel^® Xeon (TM)

or HT-enabled Intel Pentium^® 4 processor. With Hyper-Threading Technology enabled, the system treats a physical processor as two ``logical'' processors. Each logical processor is allocated a thread on which to work, as well as a share of execution resources such as cache memories, execution units, and buses.

Hyper-Threading Technology can be employed on a PC that is equipped with the following components:

an Intel Xeon or HT-enabled Intel Pentium 4 processor
a chipset that supports HT Technology
a system BIOS that supports HT Technology

SCO OpenServer supports the use of Hyper-Threading on both uniprocessor (UP) and multiprocessor (MP) systems.

Note that most SCO OpenServer commands treat logical processors as physical CPUs. Depending on whether or not Hyper-Threading is enabled, the view that commands provide of your system will be different. For example:

Dual-processor system with Hyper-Threading disabled

# cpuonoff -c
CPU1: active
CPU2: active
# uname -X | grep NumCPU
NumCPU = 2

Dual-processor system with Hyper-Threading enabled

# cpuonoff -c
CPU1: active
CPU2: active
CPU3: active
CPU4: active
# uname -X | grep NumCPU
NumCPU = 4

When you use Hyper-Threading Technology with SCO OpenServer, you will most likely see system performance improvements. Depending on the workload applied to the system, however, it is possible you could see a decrease in performance. You will probably want to run some system benchmarks with Hyper-Threading enabled and disabled to determine which offers the optimal configuration for your system.

Configuration

By default, support for Hyper-Threading is installed, but not enabled. To enable HT support:

Add the following line to the file /etc/default/boot:
```
   ENABLE_JT=Y
```
Reboot the system to rebuild the kernel:
```
   shutdown -i6 -g0 -y
```
As the system reboots, enter the system BIOS utility to enable hyperthreading in your system BIOS. (See the hardware manufacturer's documentation for details.) Save the BIOS configuration and reboot.
After the system boots, use the psrinfo(ADM) command to check processor status.

Licensing

SCO OpenServer does not distinguish between physical and logical processors. The SCO OpenServer base operating system license covers use of the physical boot processor and, by association, it's corresponding logical processors. For a single-CPU system, you can use Hyper-Threading without providing a license for additional CPUs. To take advantage of Hyper-Threading on auxiliary processors on a multi-processor system, you must purchase Additional CPU licenses. Each physical auxiliary processor requires a CPU license, and that license then supports all of the logical processors on the corresponding auxiliary processor.

Limitations

This implementation of Hyper-Threading only works on a system that provides MPS tables in the BIOS. Newer Pentium 4 systems that only provide ACPI tables will not work with SCO OpenServer's Hyper-Threading implementation.

Files