AMD APP OpenCL SDK on Intel

Question

I have seen that AMD APP SDK samples work on a machine having only Intel CPU. How can this happen? How does the compiler target a different machine architecture? Do I not need Intel's set of compilers for running the code on the intel CPU?

I think if we have to run an OpenCL application on a specific hardware, I have to (re)compile it using device's vendor specifics compiler.

Where is my understanding wrong?

Answer 1

Firstly, OpenCL is built to work on CPU's and GPU's. You can compile and run the same source code on either type of device. However, its very likely that CPU code will be sub-optimal for a GPU and vice-versa.

AMD H/W is 7% - 14% of total x86/x64 CPU's. So AMD must develop compilers for both AMD and Intel chips to be relevant. AMD have history developing compilers for both sets of chips. Conversely, Intel have developed compilers that either don't work on AMD chips or don't work that well. That's no surprise.

With OpenCL, the AMD APP SDK is the most flexible it will work well on AMD and Intel CPU's and AMD GPUs. Intel's OpenCL SDK doesn't even install on AMD x86 H/W.

If you compile an OpenCL program to binary, you can save and reuse it as long as it matches the OpenCL Platform and Device that created it. So, if you compile for one device and use on another you are very likely to get an error.

Answer 2

The power of OpenCL is abstracting the underlaying hardware and offer massive, parallel and heterogeneous computing power.

Some SDKs and platforms offers some specific features to "optimize" the code, i honestly think that such features are just marketing and they introduce boilerplate code making the application less portable.

There are also some pseudo-new technologies that are just wrappers to OpenCL or they are really similar in the concept like the Intel quick sync .

About Intel i should say that at the first place they were supporting all the iCore generation and even some C2D, now the new SDK only support the 3rd iCore generation, i don't get their strategy honestly, probably Intel is the last option if you want to adopt OpenCL and targeting the biggest possible audience, also their SDK doesn't seems to be really good at all .

Stick with the standard and you will avoid both possible legal and performance issues and your code will also be more portable.

Answer 3

The bottom line is that the AMD SDK includes a compiler for targeting x86 CPUs for OpenCL. That means that even though you are running an Intel CPU the generated code will run on it. It's the same concept as compiling a C program to run on an x86 CPU: it works on Intel and AMD CPUs (or any that implement the x86 instruction set).

The vendor's compiler might have specific optimizations, like user827992 mentions, but in my experience the performance of AMD's CPU compiler isn't that bad when running on an Intel CPU. I haven't tried Intel's OpenCL implementation.

It is true that for some (maybe most in the future) hardware, only the vendor's compiler will support it. AMD's SDK won't build code that will run on an NVIDIA card, and vice-versa. CPUs happen to be a bit of a special case in that the basic instruction set is so widely deployed that the CPU compiler will work on most machines you're likely to come in contact with.