Does AVX512 provide acceleration on all CPUs? Or some models support it but without acceleration?

[simonebaracchi]

I tried benchmarking AVX512 with various CPUs and came up with inconsistent results. I have yet to fully dig in the possible causes of this (maybe they are unrelated to the CPU), but documentation on performance expectations of AVX512 is not very wide and not conclusive.

For example, recent AMD CPUs (>= Zen4 "Genoa") do support AVX512, but my testing suggests that while the instruction set works, in the CPU models I tested it gives no performance boost over using AVX2 (or anyway the improvement is much less than the expected 2x improvement). 

My benchmarks on Intel CPUs are not conclusive. In some cases I do not see improvements also for Intel CPUs, but in my test it's still unclear whether the performance is limited by the CPU or by something else. 

My question is: are there Intel CPUs that support the AVX512 instruction set, but don't offer performance improvements over AVX2 (similar to some AMD)? Or are there different CPUs that offer various degrees of improvement over AVX2? 

Or can I expect a 2x improvement over AVX2 with every individual CPU model that supports AVX512, assuming that the workload/benchmark is able to fully utilize it? 

[VonM_Intel]

Hi, simonebaracchi.

Thank you for posting in the Intel Communities. Let me help you with that.

Please be advised that not all Intel CPUs that support AVX512 have the same features and performance. Depending on the workload and the benchmark, different CPUs may show different degrees of improvement over AVX2 using AVX512.  

Therefore, it is not possible to expect a 2x improvement over AVX2 with every individual CPU model that supports AVX512, as the performance depends on the specific extensions, the workload, and the benchmark. To find out which processors support which AVX512 variants, you can use the Intel Product Specification Advanced Search.

For more information about the Intel® Advanced Vector Extensions (Intel® AVX and AVX2), you may visit these links/articles:

• How to Know If My Intel® Processor Supports Intel® Advanced Vector Extensions 2 (Intel® AVX2)
• Does a Processor with AVX2 or AVX-512 Support AVX Instructions?
• Intel® Advanced Vector Extensions (Intel® AVX and AVX2)

You may also visit this exact link where you can find a list of Intel Processors with AVX-512 and AVX2:

• Find a list of Intel® Processors with AVX-512
• Find a list of Intel® Processors with AVX2

Best regards,

Von M.

Intel Customer Support Technician

[simonebaracchi]

Hi VonM_Intel,

Thank you for your answer.

Can I ask you more details on how to identify AVX512 "variants"?
From the provided links, I can only check whether AVX512 is supported or not, but they don't seem to provide additional details about AVX512 "variants", i.e. if I can expect a maximum of 2x performance improvements under the right testing circumstances or not.

For example, in my tests, the Intel Xeon Silver 4314 does provide an almost 2x acceleration when using AVX512, and the specs page confirms its support. 

While the Intel Xeon Gold 6226R in my tests does not provide such acceleration, but according to specs page, it supports AVX512 just like the Xeon Silver 4314.

Neither of them appear in the "Find a list of Intel® Processors with AVX-512" list.

Is there documentation about which AVX512 "variant" does each processor support?

[VonM_Intel]

Hi, simonebaracchi.

Thank you for your reply. We would like to ask you, what is the specific model of the Intel Processor that you are referring to? This will help us to check and review the documentation about the AVX-512 variant that you are asking for.

Best regards,

Von M.

Intel Customer Support Technician

[simonebaracchi]

I mentioned them in my previous message:

• Intel Xeon Silver 4314 - almost 2x acceleration 
• Intel Xeon Gold 6226R - almost no acceleration

Both of them support AVX512.
But why one performs better than the other?

[VonM_Intel]

Hi, simonebaracchi.

Thank you for the information provided.  

We will proceed to check the issue with our team internally and post back soon with more details. 

Best regards,

Von M.

Intel Customer Support Technician

[VonM_Intel]

Hi, simonebaracchi.

Please be informed that we have a forum category for the specific issues related to your product. This category is monitored by our experts who can provide you with the best solution. To help you get your answer more quickly, we will now move your post to that category.

Best regards,

Von M.

Intel Customer Support Technician

[IntelSupport]

Hello Simonebaracchi,

Please allow us some time to review the details and we will get back with an update shortly.

Regards,

Salman

[Sreelakshmi1]

Hello Simonebaracchi,

Good day!

Please accept our sincere apologies for the delay in response caused.

As you were looking for documentation about which AVX512 "variant" does each processor support, we request you to refer the below link for reference.

https://www.cpu-world.com/CPUs/CPU.html

Kindly select the Manufacturer as Intel and select the Family as per your requirement and you will be able to find the AVX512 variant details for the processors.

Also, as you were checking the reason why Intel Xeon Silver performs more than Intel Xeon gold even though both supports AVX512, it depends on factors such as workload characteristics and microarchitecture and it varies for different CPU models.

Please be informed that a 2x improvement over AVX2 is theoretically possible with AVX512, it's not guaranteed for every individual CPU model or workload.

Please let us know if you have any questions.

Regards,

Sreelakshmi B

[Sreelakshmi1]

Hello Simonebaracchi,

Good day!

We are checking if you were able to find the information we provided earlier regarding AVX512.

Regards,

Sreelakshmi.

[simonebaracchi]

Hello,

Where can I find the "AVX512 variant details for the processors" ?

For the CPUs I mentioned in my previous post, the details are at 

https://www.cpu-world.com/CPUs/Xeon/Intel-Xeon%204314.html

and

https://www.cpu-world.com/CPUs/Xeon/Intel-Xeon%206226R.html

Both pages only mention "AVX-512 / Advanced Vector Extensions 512" is supported, but nothing else about AVX512.

[Sreelakshmi1]

Hello Simonebaracchi,

Good day!

We would like to inform you that Advanced Vector Extensions 512 (Intel AVX-512) instruction set in 3rd Gen Intel® Xeon® Scalable processors that can help meet your most demanding computation challenges. As you were checking for AVX512 variants, please go through the below details.

Intel® Advanced Vector Extensions (Intel® AVX and AVX2)

Intel® AVX is a 256-bit instruction set extension to Intel® SSE designed for applications that are Floating Point (FP) intensive. Intel AVX improves performance due to wider vectors, new extensible syntax, and rich functionality. Intel AVX2 was released in 2013, extending vector processing capability across floating-point and integer data domains. This results in higher performance and more efficient data management across a wide range of applications. Examples are image and audio/video processing, scientific simulations, financial analytics, and 3D modeling and analysis.

Intel® Advanced Vector Extensions 512 (Intel® AVX-512)

The Intel® AVX-512 enables processing of twice the number of data elements that Intel AVX/AVX2 can process with a single instruction and four times the capabilities of Intel SSE. Intel AVX-512 instructions are important because they open up higher performance capabilities for the most demanding computational tasks. Intel AVX-512 instructions offer the highest degree of compiler support in the design of the instruction capabilities. Please be informed that the AVX-512 Variant is not available for Processors.

Please refer the below article for reference.

https://www.intel.com/content/www/us/en/architecture-and-technology/avx-512-solution-brief.html

Regards,

Sreelakshmi

[Sreelakshmi1]

Hello Simonebaracchi,

Good day!

We are checking if you were able to find the information we provided earlier.

Regards,

Sreelakshmi.

[Sreelakshmi1]

Hello Simonebaracchi,

Greetings for the day!

We would like to inform you that we are closing this request as no response has been received from our previous follow-ups. Please don't hesitate to ask any further questions in the future. Feel free to start a new conversation, as this thread will no longer be monitored.

Best regards, 

Sreelakshmi

[simonebaracchi]

As I understand it, there are no AVX-512 "variants". 

Processors that are capable of AVX-512 are expected to be 2x faster than AVX-2, which is 2x faster than AVX and so on. 

Other differences might lie in the cache speed, clock speed, software optimizations and so on.

But there are no "fast or slow variants" of AVX-512.

[Azeem_Intel]

Hello Simonebaracchi,

Greetings for the Day!

I hope you are doing well. Yes, we also referred you to the above article. Kindly review the article for more information on this case.

Please do not hesitate in contact us, we are more than glad to assist you.

Best Regards,

Azeem_Intel

[Sreelakshmi1]

Hello Simonebaracchi,

Good day!

Please let us know if you need any further assistance regarding your query. If not, please confirm if we can proceed to close the request."

Regards,

Sreelakshmi.

[simonebaracchi]

Let's close the request, thank you