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templex
Novice
300 Views

How to detect microarchitecture on Xeon Scalable?

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Some Xeon CPUs share the same family and model code but has different microarchitecture.

 

What I want is to detect the microarchitecture by instruction like CPUID or something else.

 

I found Xeon Scalable 's crystal frequency's behavior is different on different microarchitectures:

1. On Skylake, its actual frequency by (approximately) -0.25%

2. On Cascade Lake, the frequency is stable (25 MHz) (I'm not really sure about that, see question: here)

 

So I want to get the microarchitecture on Xeon.

 

Thank you!

 

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HadiBrais
New Contributor III
257 Views

This information can be found in the specification update documents of the processors that implement a given microarchitecture. For example, for SKL-SP, the specification update document can be found at: https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-scalable-spe.... There can be multiple specification update documents for different collections of processors that implement the same microarchitecture.

The specification update documents usually only list the CPUID information for boxed processors, not tray processors, so they don't really provide a complete of stepping IDs. For example, stepping ID 0x3 mentioned in my earlier post is for tray SKL-SP processors. There can be other stepping IDs that I'm not aware of. If you care about both boxed and tray processors, you can contact Intel for a complete list of CPUID information.

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HadiBrais
New Contributor III
287 Views

The stepping ID (which is the lowest 4 bits of CPUID.(EAX=0x1, ECX=0x0):EAX) for CSL-SP is 0x7 while the stepping IDs for SKL-SP are 0x2, 0x3, and 0x4.

templex
Novice
264 Views

Thank your for your help, it really helps me a lot.

 

And I wonder where could I found the stepping ID table? What I mean is a list of stepping IDs and microarchitecture.

 

Thanks

HadiBrais
New Contributor III
258 Views

This information can be found in the specification update documents of the processors that implement a given microarchitecture. For example, for SKL-SP, the specification update document can be found at: https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-scalable-spe.... There can be multiple specification update documents for different collections of processors that implement the same microarchitecture.

The specification update documents usually only list the CPUID information for boxed processors, not tray processors, so they don't really provide a complete of stepping IDs. For example, stepping ID 0x3 mentioned in my earlier post is for tray SKL-SP processors. There can be other stepping IDs that I'm not aware of. If you care about both boxed and tray processors, you can contact Intel for a complete list of CPUID information.

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