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Need help with SMI, Intel Core i5-1135G7 CPU, and SMI induced latencies.

_devin_
Beginner
719 Views

Hello,

I'm new to this forum so kindly let me know if I should be posting these questions somewhere else.

I have two laptops:

  • Lenovo ThinkBook Gen 2
  • Dell Latitude 5420

Both laptops have an Intel Core i5-1135G7 CPU.

I'm monitoring SMI by reading MSR register 0x34 (SMI Counter). I assume that this counter can only be incremented when there's an SMI.

The Lenovo laptop is not generating any SMI when running our real-time application. The Dell is generating an SMI roughly every 14.648 seconds. Both laptops have the same bits set in the SMI Control and Enable register (SMI_EN, offset 0x30):

  • 28: eSPI SMI Enable (ESPI_SMI_EN)
  • 13: TCO Enable (TCO_EN)
  • 1: End of SMI (EOS)
  • 0: Global SMI Enable (GBL_SMI_EN)

The latency caused by the SMI on the Dell is usually over 1 ms (i.e. the OS and all our application code pauses during this time).

As a side note, I can also see this latency when running the Intel BIOS Implementation Test Suite (BITS) SMI Latency test. On the Lenovo, there's zero SMI and the latency is <150 us so it passes the test. Based on other testing, the latency on the Lenovo appears to be about 7 us with this type of SMI Latency test. The same SMI Latency test fails on the Dell and has one SMI. The latency on the Dell is over 2 ms when running the BITS SMI Latency test. If I modify the BITS SMI Latency test to run for only 3 seconds instead of 15 seconds, then the Dell has zero SMI and a latency of about 5 us.

Some preliminary questions are:

- Is the SMI Counter (MSR register 0x34) only incremented when there is an SMI?

- Is there a way to determine the cause of an SMI? Since only TCO and eSPI are enabled, it must be one of them but is there a way to determine which one?

- Is TCO SMI only used for Watch Dog Timers (WDT)? If it generates an SMI then should I expect the system to reboot in that case? I don't have any WDT drivers enabled that would be utilizing the TCO SMI. Should TCO SMIs be disabled by default unless some driver sets it up?

- The SMI seems to occur periodically every ~14.648 seconds. Could that give me any more clues about the cause?

- I've never used eSPI before but it looks like a bus. Is there a way to query/determine what's on the bus that might be causing these SMI?

- It looks like the TCO SMI is enabled and locked so that I cannot disable it. Is there a similar mechanism for eSPI that is preventing me from disabling the eSPI SMI?

I guess that's it for now. Any other guidance/advice would be appreciated. I've created a case with Dell but it doesn't seem to be going anywhere (yet). Ideally, I would like to remove/prevent the periodic SMI on the Dell laptop.

Thanks,
Devin

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8 Replies
Alberto_R_Intel
Moderator
688 Views

_devin_, Thank you for posting in the Intel® Communities Support.


In reference to your questions, we will be more than glad to assist you with this matter or point you in the right direction in order for you to gather the information that you are looking for.


For us to try to provide the most accurate technical support on this topic, we just wanted to confirm, what do you mean by SMI?

Is it:

System Management Interrupt?

Structure of Management Information?

Service Measurement Index?

Storage Management Initiative?


Any questions, please let me know.


Regards,

Albert R.


Intel Customer Support Technician


_devin_
Beginner
681 Views

Hi Albert,

By SMI, I mean System Management Interrupt.

Thanks,

Devin

Alberto_R_Intel
Moderator
669 Views

_devin_, Thank you very much for confirming that information.


We will do further research on this matter, as soon as I get any updates I will post all the details on this thread.


Regards,

Albert R.


Intel Customer Support Technician


Alberto_R_Intel
Moderator
658 Views

Hello _devin_, I just received an update on this matter.


After reviewing the case and based on the fact that you are running your own application, the best course of action will be to submit your question to the Intel Developer Zone. In there you will find personalized content, leverage Intel's design, and support for developers and other peers:

https://software.intel.com/content/www/us/en/develop/home.html


Regards,

Albert R.


Intel Customer Support Technician


_devin_
Beginner
656 Views

Hi Albert,

What's the difference between the Intel Developer Zone and this forum?

Would you provide me with a link to a form that I can fill out to submit my questions to (or guide me through the URL that you provided previously)?

Thanks,
Devin

Alberto_R_Intel
Moderator
628 Views

Hi _devin_, Thank you very much for your response.


"What's the difference between the Intel Developer Zone and this forum?" The difference is that by submitting your question to the Intel® Developer Zone, you will be talking to software developers/peers and subject matter experts that will be able to provide the most accurate technical assistance on this topic.


"Would you provide me with a link to a form that I can fill out to submit my questions to", Yes, sure, in the following link you will be able to register, login and submit your question in our Intel® Developer Zone support for further assistance on this matter:

https://www.intel.com/content/www/us/en/forms/idz/simple-registration.html


Regards,

Albert R.


Intel Customer Support Technician


_devin_
Beginner
619 Views

Hi Albert,

 

I've reposted this question to the Software category under these same forums:

https://community.intel.com/t5/Software-Tuning-Performance/Need-help-with-SMI-Intel-Core-i5-1135G7-C...

 

Thanks,

Devin

Alberto_R_Intel
Moderator
608 Views

Hi _devin_, Thank you very much for providing those updates.


Perfect, no problem, that is also an option, you will also find peers in there as well that will be able to further assist you with this subject.


Any other inquiries, do not hesitate to contact us again.


Regards,

Albert R.


Intel Customer Support Technician


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