Win2k + Hyperthreading?

[Yoni]

I've seen places on the Internet claim hyperthreading on Win2k is futile since Win2k doesn't support it, so wouldn't see performance gains, as opposed to XP and 2k3.

This doesn't sound right to me, since hyperthreading is supposed to be simply having the processor emulate 2 processors, and the OS using a dual-processor kernel, without requiring any special software optimizations.

Please prove me wrong (preferably by referring to a document written by Microsoft or Intel).

[Mephisto]

I don't have a document, only experience.  I used both Windows Server 2003 and Windows XP Professional.  Hyperthreading worked great on both.  When multi-tasking (such as having bots loaded, defragmenting, burning a CD, and playing a game) CPU usage stayed from 0 - 10% on both XP/2k3.  On Windows 2000 Professional/Server however, when doing the same type of multi-tasking on the same machine, CPU usage was often at around 25 - 75%.  I suspect this is due to the fact that 2k3 doesn't support HT as well as XP/2k3 since all of the settings were the same and it was on the same hardware/machine.

[Adron]

IIRC, Win2k doesn't properly give up cpu resources when one of the virtual cpus doesn't need to run. There are some new instructions to do that.

[Mephisto]

Please prove me wrong (preferably by referring to a document written by Microsoft or Intel).

This document doesn't go into very much detail as far as explaining the whys and hows, but it does give an overview of which operating systems are optimized for Intel hyperthreading technology.  You can also do some quick MSN searches to find documents (not by Microsoft or Intel) detailing on the whys/hows as to why Windows 2000 doesn't support hyperthreading as well as Windows XP or Windows Server 2003.
http://www.intel.com/support/platform/ht/os.htm

[Yoni]

Hmmk, thanks.