The trouble with hyperthreading

If you spend time reading through the mailing lists relating to multi-threaded programs running on Linux systems, you will find that it has been found that multi-threaded programs, such as the proxy in CNv4, run better if hyperthreading is switched off.

You can tell whether your processor may be running in hyperthreaded mode by checking the available flags it supports.

To do this run the following command :-

grep flags /proc/cpuinfo

You may get output similar to the following

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl est cid cx16 xtpr lahf_lm

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl est cid cx16 xtpr lahf_lm

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl est cid cx16 xtpr lahf_lm

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm constant_tsc pni monitor ds_cpl est cid cx16 xtpr lahf_lm

This output shows a machine with four processors (because there are four lines). The important point to note is the presence, or absence, of the ht flag. We have shown it in bold above so that it stands out, but the output you receive won't have that benefit.

The presence of the ht flag only indicates that your processor is capable of supporting hyperthreading, not that it is doing so.

What you need to do is reboot your CensorNet and press the appropriate button to enter the BIOS as the machine starts to come back up.

If you find the word "hyperthreading" in your BIOS, make sure it is disabled.

Some manufacturers don't call it hyperthreading. The following screen shot is from the BIOS on a Dell system.

The important setting here is "Logical Processor" and you need to change the setting to "Disabled".

Once you have modified your BIOS, save the settings and exit, the system should boot normally.

Ocassionally, a BIOS simply offers no means to change a relevant setting. If this is the case, type the following at the command line :-

cat /proc/cpuinfo

Copy the output you receive into an email and send it to support@censornet.com