Re: Intel Hyper Threading

On Sat, 22 Mar 2008 05:37:08 GMT, "whodunit"
<nul@localhost.org> wrote:

>I have an issue with a board where the CPU indicates it has Y number of 
>logical processors, and X number of cores.  However, enabling and disabling

>Hyper Threading in the BIOS will not make a difference to the number of 
>actual processors that are visibile -- X, not Y.  It seems to me there ought

>to be a machine specific register (MSR) feature bit that controls Hyper 
>Threading, a bit that is not being toggled to enable HT.  Does anyone know 
>where to find the necessary information about enabling HT via an MSR, and 
>which register and bit(s) this would be?
>
>I already know about APIC, the CPUID feature bits in EDX, and the logical 
>versus physical core counts in CPUID values.  What I am looking for is 
>another bit, or bits, elsewhere that truly enables HT.
>
>Thanks, 
>

Is it safe to assume you have ruled out other factors like
whether HT was enabled when the OS was installed?

It might not hurt to list the hardware and OS.

I have an issue with a board where the CPU indicates it has Y number of 
logical processors, and X number of cores.  However, enabling and disabling 
Hyper Threading in the BIOS will not make a difference to the number of 
actual processors that are visibile -- X, not Y.  It seems to me there ought 
to be a machine specific register (MSR) feature bit that controls Hyper 
Threading, a bit that is not being toggled to enable HT.  Does anyone know 
where to find the necessary information about enabling HT via an MSR, and 
which register and bit(s) this would be?

I already know about APIC, the CPUID feature bits in EDX, and the logical 
versus physical core counts in CPUID values.  What I am looking for is 
another bit, or bits, elsewhere that truly enables HT.

Thanks, 

"whodunit" <nul@localhost.org> wrote in message 
news:7W0Fj.59884$cQ1.37949@bgtnsc04-news.ops.worldnet.att.net...
>I have an issue with a board where the CPU indicates it has Y number of 
>logical processors, and X number of cores.  However, enabling and disabling

>Hyper Threading in the BIOS will not make a difference to the number of 
>actual processors that are visibile -- X, not Y.  It seems to me there 
>ought to be a machine specific register (MSR) feature bit that controls 
>Hyper Threading, a bit that is not being toggled to enable HT.  Does anyone

>know where to find the necessary information about enabling HT via an MSR, 
>and which register and bit(s) this would be?
>
> I already know about APIC, the CPUID feature bits in EDX, and the logical 
> versus physical core counts in CPUID values.  What I am looking for is 
> another bit, or bits, elsewhere that truly enables HT.
>
> Thanks,
>

yaaawwwwnnnnnnnnnnnnnnnnnnnnn 

>>I have an issue with a board where the CPU indicates it has Y number of
>>logical processors, and X number of cores.  However, enabling and 
>>disabling
>>Hyper Threading in the BIOS will not make a difference to the number of
>>actual processors that are visibile -- X, not Y.  It seems to me there 
>>ought
>>to be a machine specific register (MSR) feature bit that controls Hyper
>>Threading, a bit that is not being toggled to enable HT.  Does anyone
know
>>where to find the necessary information about enabling HT via an MSR,
and
>>which register and bit(s) this would be?
>>
>>I already know about APIC, the CPUID feature bits in EDX, and the
logical
>>versus physical core counts in CPUID values.  What I am looking for is
>>another bit, or bits, elsewhere that truly enables HT.
>>
>>Thanks,


> Is it safe to assume you have ruled out other factors like whether HT was 
> enabled when the OS was installed?
>
> It might not hurt to list the hardware and OS.


For the sake of argument, let us say the OS is the venerable MS DOS, and 
that my program is able to identify and run threads on all active 
processors.  From the above statement, it is known that Y logical processors 
is exactly twice the number of X physical cores.  Both values are available 
from the CPUID instruction.

The initial boot attempt with Linux (kernel 2.6.22) was not successful with 
the CPU is its current socket, so I will attempt to move it to another 
socket this afternoon and check if Linux is able to boot.  The problem 
yesterday afternoon was that Linux could not start CPU 0, according to the 
screen.

I cannot divulge the processor, except to say it is from Intel.  I merely 
seek knowledge about any MSRs that control Hyper Threading, if they exist, 
so I can make full use of the processor as it advertises its capable of. 

whodunit wrote:

> I have an issue with a board where the CPU indicates it has Y number of
> logical processors, and X number of cores.  However, enabling and
> disabling Hyper Threading in the BIOS will not make a difference to the
> number of
> actual processors that are visibile -- X, not Y.  It seems to me there
> ought to be a machine specific register (MSR) feature bit that controls
> Hyper
> Threading, a bit that is not being toggled to enable HT.  Does anyone know
> where to find the necessary information about enabling HT via an MSR, and
> which register and bit(s) this would be?
> 
> I already know about APIC, the CPUID feature bits in EDX, and the logical
> versus physical core counts in CPUID values.  What I am looking for is
> another bit, or bits, elsewhere that truly enables HT.
> 
> Thanks,

If the kernel isn't smp aware, it'll never make use of the feature. I
suggest you use a recent kernel, 2.6.23.3 and enable the needed features.





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