- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
I've found that the RDTSC instruction only ever returns even values on several of the chips I have access to. These include:
Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
2.4 GHz 8-Core Intel Core i9
Intel(R) Xeon(R) CPU E3-1275 v6 @ 3.80GHz
Intel(R) Core(TM) i5-7500 CPU @ 3.40GHz
However, there are some chips that return both even and odd values:
Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz
Intel(R) Xeon(R) CPU E5-2667 0 @ 2.90GHz
I'm running on various versions of the linux kernel including 4.4.12, 4.4.111, 5.4.72.
This occurs both when calling rdtsc() from inside the kernel as well as the attached user-space program. No matter when/where I call RDTSC and no matter how many times I do so and no matter what I put in-between those calls -- they are always even values.
This behavior seems broken. Did something go wrong with all the various tweaks to TSC behavior that have occurred over the years? Or is this just an expected side-effect of various CPU instruction processing optimizations?
Link Copied
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hello rerickson,
Thank you for posting your question on this Intel® Community.
To better assist you, I would like to gather additional information about this behavior.
- What is the Linux distribution(s) you are using?
- Are you currently developing software?
- How is this behavior impacting your project/environment?
Regards,
Wanner G.
Intel Server Specialist
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Our linux distribution is “home-grown” (so difficult to quantify) but based on Debian.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hello rerickson,
Thank you for providing additional details about your project.
For Software Development inquiries, our recommendation is that you submit your questions to the Intel® Developer Zone.
Intel® Developer Zone - Contact Page
https://software.intel.com/en-us/support
You can submit your ticket through the Online Service Center at https://www.intel.com/supporttickets for support.
See How to Create a Support Request at the Online Service Center.
https://software.intel.com/en-us/articles/how-to-create-a-support-request-at-online-service-center
Regards,
Wanner G.
Intel Server Specialist
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
I just want to make sure I'm understanding this. CPU instructions themselves are considered software and *not* hardware related?
For example, if I were to call the CPUID instruction and the bits it returned didn't match the physical specs for that chip then it would be a software problem?
I understand that for a company like Intel that does such a wide range of hardware and software that the distinction between the two is different than what I might expect.
Are you assuming that this *must* be a problem with the assembler? How come the exact same output works on some Intel chips but now others? Given that we're talking about a CPU instruction (and not something "fancy") how is that not a HW issue?
Please help me to understand how you're making the HW vs SW distinction in this case.
Thanks
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
Hello rerickson,
Thank you for your response.
"CPU instructions themselves are considered software and *not* hardware related?"
I would like to clarify that this is not what I meant.
Depending on the inquiry you have, and since you are currently working on a software development project, a different support channel would be recommended.
In this scenario, our recommendation is that you submit your question to the Intel® Developer Zone to obtain additional support for this inquiry.
Wanner G.
Intel Server Specialist
- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page