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Hyper-Threading
Hyper-Threading is a technology found in the Intel® Xeon™ processors. Using Hyper-Threading, a single Hyper-Threading enabled processor can simultaneously process two threads of code, improving the performance of multi-threaded code running on a single processor platform. In essence, Hyper-Threading Technology partitions a single processor into two logical processors.
Because Hyper-Threading might reduce the performance of certain application significantly, this feature is disabled by default. ASL highly recommends that one should spend some times to benchmark the application(s) running with and without Hyper-Threading first. If time does not permit, Hyper-Threading should be left disabled. In general, Hyper-Threading works best in the server environment.
To enable Hyper-Threading, perform the following steps:
Enable Hyper-Threading under the Advanced->Processor Features menu in the BIOS.
Add the kernel parameter acpismp=force to the Linux boot loader (LILO/GRUB). If LILO is used, it is necessary to run lilo after making the change to /etc/lilo.conf.
When Hyper-Threading is enabled, the BIOS and Linux will report a total of four processors in a dual processor system.
Linux
ASL 2.4.19-4 kernel
or higher is required for best functionality. Do not use the Red Hat kernels
since they do not handle system interrupts properly on the Intel dual
Xeon platforms.
Beside bug fixes, driver enhancement and added functionality, ASL kernels
outperformance stocked Red Hat kernels by significant margin. As shown below,
system performance is up to 20 times faster when using an ASL kernel.
Extracting a kernel source tree on an Intel Xeon platform with Hyperthreading:
Time / Kernel (smaller is faster)
8m 30s (Red Hat 2.4.7)
1m 20s (Red Hat 2.4.18-3)
0m 04s (ASL 2.4.18-7)
The kernel parameters ide0=ata66 ide1=ata66 must be enabled
in the boot loader. If LILO is used, add the entry to /etc/lilo.conf. If GRUB is
used, add the entry to /etc/grub.conf.
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