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Does disabling Hyper Threading require a rebuild of Win2k Advanced server

Posted on 2004-12-01
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I have a 4 CPUs machine with hyper threading enabled. I have  Win2k Advanced version installed and OS reports  8 processors correctly. I want to disable hyper threading in BIOS but do I need to rebuild the server?  

Thanks,
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Question by:jgmoras
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by:InteraX
ID: 12720925
Hi jgmoras,

Most likely not. Because you already have the SMP kernel loaded, it shoudln't matter whether HT is enabled or not.

Good Luck!
;-)
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by:jgmoras
ID: 12721042
The reason I asked, because with HTenabled  and while loading OS, the OS counts all logical processors and in this case the count was 8. It is true it has  SMP kernel loaded but still it is not exactly the same when used in context of HT.  I could not find any pertinent link on Microsoft's web site.  have not done in real life and was wondering if anyone has done it for sure    
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by:InteraX
ID: 12721129
I haven't done this with AS, or with more than 1 processor, but when you disable it on a single processor system, the OS only counts 1 processor. The only difference should be the number of processors the OS will see.
MS have produced a doc on Windows servers and HT.
http://www.microsoft.com/windows2000/docs/hyperthreading.doc
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by:Netman66
ID: 12721402
You'll have no problems.  The count will be four, but the HAL is still the same - this is what InteraX is hinting at.

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by:Netman66
ID: 12721415
Oh...incidently, if you're concerned about per-processor licensing - it's per physical processor, not virtual.

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by:jgmoras
ID: 12755486
Folks,

My concerns  are not  with HAL and license count. Initially when OS was built with HT enabled, kernel built the OS with 8 processors. Now with HT disabled, will not kerel expect 8 processors? I think one may have to tweak boot ini and put no. of processors as 4.

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by:Netman66
ID: 12755718
No.  Multiprocessor is 2 and up.  Same HAL, same Kernel.

Boot.ini should have no information on processors.

As with anything, backup everything before you make the change - I do not expect you to have any problems.




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by:Netman66
ID: 12755780
I should add this.  If (for some reason) you have partitioned off the hardware using the virtual CPUs for the apps then you could have a problem.  However, I'm not even certain you can partition virtual hardware - I imagine it's physical hardware only (in which case you're fine).

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by:jgmoras
ID: 12758990
The switche that can be used in Boot.ini

/numproc=number
This switch sets the number of processors that Windows will run at startup. With this switch, you can force a multiprocessor system to use only the quantity of processors (number) that you specify. This switch can help you troubleshoot performance problems and defective CPUs.


http://support.microsoft.com/default.aspx?scid=kb;en-us;833722

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by:Netman66
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He got his answer.
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