topic Hi, thanks for responding. in Software Archive

Which processors support vt-d Posted Interrutps?

Bratterud__Alfred — Wed, 15 Nov 2017 18:38:14 GMT

We're starting a project where vt-d posted interrupts, as specified in [1] §5.2 will be a core component and we need to acquire the correct processors / mainboards. I can see from [2] that E5-2600 v4 chips were announced with this feature - can I assume that all later chips with vt-d support also support it? If not, how can I find out which processors that do?

I'm interested in Xeon E5 v4 and later, including the new Xeon Bronze-Platinum spectrum. I couldn't find any information in the vt-d spec, the manual (Vol.3 §29) or in other forum posts [3-5] that helps identify the concrete processors that ships with this feature. In post [3] it's mentioned that you need to make sure to get the correct CPU / motherboard combination, but then links to another post addressing vt-d support in general.

[1] https://www.intel.com/content/www/us/en/embedded/technology/virtualization/vt-directed-io-spec.html
[2] https://www.theregister.co.uk/2016/03/31/intel_broadwell_ep_xeon_e5_2600_v4/?page=2
[3] https://software.intel.com/en-us/forums/virtualization-software-development/topic/673618
[4] https://software.intel.com/en-us/forums/virtualization-software-development/topic/543398
[5] https://software.intel.com/en-us/search/site/language/en?query=posted+interrupts

Hello,

Quoc-Thai_L_Intel — Wed, 15 Nov 2017 21:01:14 GMT

Hello,

If you know the processor that you have, you can use this website to find out more details about the processor. Vt-d is one of the items on the list of technologies. Here are two examples:

https://ark.intel.com/products/96900/Intel-Xeon-Processor-E7-8894-v4-60M-Cache-2_40-GHz

https://ark.intel.com/products/93807/Intel-Xeon-Processor-E5-4667-v4-45M-Cache-2_20-GHz

Regards,

-Thai

Hi, thanks for responding.

Bratterud__Alfred — Wed, 15 Nov 2017 21:49:00 GMT

Hi, thanks for responding.

As I mentioned in the original post I'm not asking which CPU's have vt-d, but rather which CPU's have vt-d posted interrupts. Intel vt-d was documented here [1] in 2012, but according to [2] vt-d posted interrupts was introduced with E5 v4 in 2016. Also as I mentioned I don't yet have the CPU but want to buy some, and would like to make sure I get the right ones. This means I can't use e.g. the cpuid instruction or OS facilities to determine whether or not I have that feature.

To rephrase the question in two parts:
1) Is posted Interrupts now a guaranteed feature of all CPU's that have vt-d? (and e.g. are newer than e.g. E5 v4)
2) If not, how can I know in advance of buying if a certain model supports posted interrupts?

Thanks again

[1] https://software.intel.com/en-us/articles/intel-virtualization-technology-for-directed-io-vt-d-enhancing-intel-platforms-for-efficient-virtualization-of-io-devices
[2] https://www.theregister.co.uk/2016/03/31/intel_broadwell_ep_xeon_e5_2600_v4/?page=2

I got some inputs from my

Quoc-Thai_L_Intel — Thu, 16 Nov 2017 22:10:59 GMT

I got some inputs from my peers. You might want to look for server segment processor with code name formerly known as Broadwell, Skylake, or later. You can identify the processor by using the website that I provided earlier. Also you will need to consider the platform support as well beside the processor. Here are some notes from one article: https://software.intel.com/en-us/articles/intel-xeon-processor-e5-2600-v4-product-family-technical-overview

Posted Interrupts

Posted Interrupts enables efficient co-migration of interrupts with virtual processors avoiding the need for a VM-exit. When a sequence of external interrupts are sent to the VM, they are treated like a posted write and stored in memory. Since posted interrupts are directly supported by the hardware there is a reduction in the number of VM-exits that occur as compared to using software to resolve the interrupt. Posted interrupts is also complimentary to APIC Virtualization, further improving virtual-interrupt performance.

Figure 13: Comparison of software-based interrupt handling against APIC Virtualization, which was introduced on Ivy Bridge, and lastly with Broadwell, which provides additional support with posted interrupt support in the hardware.

Refer to your OEM BIOS guide for instructions on setting the Intel VT-x feature in your BIOS. Contact your VMM provider to verify support of this feature.

Regards,

-Thai