Is there any way to debug OpenCL kernels on an Nvidia GPU, i.e. set breakpoints and inspect variables? My understanding is that Nvidia's tool does not allow OpenCL debugging, and AMD's and Intel's only allow it on their own devices.
gDEBugger might help you somewhat (never used it though), but other than that there isn't any tool that I know of that can set breakpoints or inspect variables inside a kernel. Perhaps try to save intermediate outputs from your kernel if it is a long kernel. Sorry I can't give you a magic solution, debugging OpenCL is just hard.
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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?
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.
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.
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.
I've been doing some research in to OpenCL, and the possibility of using it on a project. The question I have is, is there a way to run OpenCL code on a CPU that is unsupported by the OpenCL SDKs in a C++ application. I know Java has Aparapi, however I'm wondering how to run OpenCL code in a C++ application without hardware that is supported by the SDKs. There is some code I would like to write in OpenCL kernels to take advantage of the OpenCL parallelism where available, however I'm unsure if I wouldn't be able to run it on older hardware (still X86, but not recent hardware). Could anyone explain to me how this can be done, or if it is even a problem at all to run OpenCL code on older systems?
Thanks,
Peter
I would say best way to approach this is to check if the device supports OpenCL via OpenCL API calls such as clPlatformIDs then once you figure it isn't a OpenCL device then run the required code as normal C/C++ function otherwise run it using openCL kernel. But for portability you need to write the program logic twice once in .cl file and once as normal c/c++ method/function.
I am unsure to put it up, but I need an OpenCL library that can actually work under QEMU.
I have tried NVidia, and AMD but none of them seem to function there.
Does anyone have any idea?
Use the Intel's or AMD's libs, they both run on the CPU.
I have a system with an NVidia graphics card and I'm looking at using openCL to replace openMP for some small on CPU tasks (thanks to VS2010 making openMP useless)
Since I have NVidia's opencl SDK installed clGetPlatformIDs() only returns a single platform (NVidia's) and so only a single device (the GPU).
Do I need to also install Intel's openCL sdk to get access to the CPU platform?
Shouldn't the CPU platform always be available - I mean, how do you NOT have a cpu?
How do you manage to build against two openCL SDKs simultaneously?
You need to have a SDK which provides interface to CPU. nVidia does not, AMD and Intel's SDKs do; in my case the one from Intel is significantly (something like 10x) faster, which might due to bad programming on my part however.
You don't need the SDK for programs to run, just the runtime. In Linux, each vendor installs a file in /etc/OpenCL/vendors/*.icd, which contains path of the runtime library to use. That is scanned by the OpenCL runtime you link to (libOpenCL.so), which then calls each of the vendor's libs when querying for devices on that particular platform.
In Linux, the GPU drivers install OpenCL runtime automatically, the Intel runtime is likely to be downloadable separately from the SDK, but is part of the SDK as well, of course.
Today i finally got around to trying to start doing openCl development and wow... it is not straight forward at all.
There's an AMD sdk, there's an intel sdk, there's an nvidia sdk, each with their own properties (CPU only vs GPU only vs specific video card support only perhaps?)
There may be valid technical reasons for it having to be this way but i really wish there was just one sdk, and that when programming perhaps you could specify GPU / CPU tasks, or that maybe it would use whatever resources made most sense / preformed best or SOMETHING.
Time to dive in though I guess... trying to decide though if i go CPU or GPU. I have a pretty new 4000$ alienware laptop with SLI video cards, but then also an 8 core cpu so yeah... guess ill have to try a couple sdk's and see which preforms best for my needs?
Not sure what end users of my applications would do though... it doesnt seem like they can flip a switch to make it run on cpu or gpu instead.
The OpenCL landscape really needs some help...
I googled this topic and didn't find anything new. I am aware of Nvidia's FFT implementation which is great, but for CUDA only. AMD just released their implementation, but it doesn't work on Nvidia cards. Apple has an older and slower implementation. Are there any other good FFT libraries out there? It would be nice if there was an implementation that was meant to work on Nvidia and AMD cards and other possible platforms and is being actively maintained.
The AMD clAmdFft library should work on NVidia GPUs.
I was involved in the development and I know that was the intention. The code was written to the OpenCL standard and doesn't use any proprietary tricks. Of course, AMD didn't do QA testing on NVidia hardware. It could be that NVidia's OpenCL implementation isn't quite 100% compliant to the standard yet. Or it could be something about your particular video card.
Please post more details here as to exacly what is happening. You should also post that information in the AMD developer forums as a bug.
AMD recently released an OpenCL SDK for their CPUs as wel as GPUs. Included in it are FFT and BLAS libraries. You can go to the bottom of the page to find out about the supported devices.
But I am not really sure about the performance.
Not yet - but there is a project to port the GSL (Gnu Scientific Library) to opencl
http://gsl-cl.sourceforge.net/
I know Apple has released an OpenCL FFT package, but I don't know much about it. I've heard that they make the source available.