OpenCL 1.0: The Road to Pervasive GPU Computing
by Derek Wilson on December 31, 2008 6:40 PM EST- Posted in
- GPUs
Why NVIDIA Thinks CUDA for C and Brook+ Are Viable Alternatives
While OpenCL is a high level API, it does require the programmer to perform certain tasks that don't have much to do with the parallel algorithm being implemented. OpenCL devices in the system need to be found and set up to properly handle the task at hand. This requires a lot of overhead like creation of a context, device selection, creating the command cue(s), management of buffers for supplying and collecting data on the OpenCL device, and dynamically compiling OpenCL kernels within the program. This is all in addition to writing kernels (data parallel functions) and actually using them in a program that does useful work.
The overhead and management work required is similar to what goes on with OpenGL. This makes sense considering the fact that both use GPUs, they can share data with eachother, and that the same standards body that manages OpenGL is now managing OpenCL. But the fact remains that this type of overhead is cumbersome and can be a real headache for anyone who is more interested in the algorithm. Like scientists working on HPC code who know the theory much better than the programming most of the time.
Both Brook+ and CUDA for C hide the complexity of setting up the hardware by allowing the driver to handle the details. This allows developers to write a kernel, use it, and forget about what's actually going on in the hardware for the most part. Going with something like this as a first move for both NVIDIA and AMD was a good move, as it allows developers to get familiar with the type of programming they will be doing in the future for data parallel problems without tacking higher levels of complexity than necessary.
NVIDIA, for one, believes a language extension as opposed to an API like OpenCL has major benefits and will always have a place in GPU computing (and especially in the HPC space where scientists don't want to be programmers any more than they need to). When asked if they would submit their language to a standards body, NVIDIA said that was highly unlikely as there are other language efforts out there and NVIDIA has been advancing CUDA for C much more rapidly than a standards body would.
On the down side, putting more control in the hands of the developer can result in better, faster code. There is a bit of a "black box" feeling to these solutions: you put code in and get results out, but you can't be sure what goes on in the middle to make it happen. OpenCL gives you better ability to fine tune the software and make sure that exactly what you want to happen happens. Despite NVIDIA's assertions that scientists interested in coding for HPC solutions will have a better experience with CUDA, the cost/benefit of ultra-fine tuning code for HPC machines leans heavily in favor of spending the time and money on optimizing. This means that OpenCL will likely be the choice for performance sensitive HPC applications. CUDA for C and Brook+ will likely have more of a place in just trying out ideas before settling on a final direction.
So there you have it. OpenCL will enable applications in the consumer space to take advantage of data parallel hardware, while Brook+ and CUDA may still have a place in the industry as well (but not on the consumer side of things). That is, until some other more popular standard data parallel language extensions come along and pushes both CUDA for C and Brook+ out of the market.
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melgross - Thursday, January 1, 2009 - link
It's interesting that while ATI and Nvidia are heavily mentioned with their rapidly depreciating standards, Apple, which after all, developed OpenCL isn't mentioned even once, though it will also likely be the first to implement OpenCL in 10.6 later this year, possibly by March. Even their Logo isn't shown. Very strange!Wwhat - Monday, January 5, 2009 - link
By march they might (should) not be the first but graphicscard makers should have updated their drivers to support it already, after all they were well aware of OpenCL long before and already announced they would support it, and nvidia said that porting to it would be easy, plus both ATI and nvidia have no problem at all releasing unstable software/drivers, none at all, as we all experienced.Oh and nvidia had an OpenGL3 driver out in like 2 days after final specs and ATI a in a few weeks, so that makes you think they can put some steam behind their efforts if they want to.
dvinnen - Thursday, January 1, 2009 - link
The logo picture was taken from their siterdbrown - Friday, January 2, 2009 - link
On the the Khronos website right above the "Logos" Apple is the one who initially proposed the working group, Apple is also mentioned in the list of companies. They must not of posted Apple's logo knowing that everyone who knows anything about Open CL knows that it is Apple's technology, Heck Apple even owns the trademark rights.melgross - Thursday, January 1, 2009 - link
At least they should have been mentioned in the article.yyrkoon - Thursday, January 1, 2009 - link
And to say what ? That Apple feeling left out in the cold has made efforts to take the next obvious step and standardize GPU processing( very late in the game )? That is, assuming what you're saying is true.Gee, how very innovative of them.
hakime - Saturday, January 3, 2009 - link
Shut up you are trolling!! You don't know what you are talking about, period.The fact that there is not reference of Apple in the article is a serious drawback. Apple invented and designed Open CL as mush as SGI invented and designed Open GL, ignoring it is simply wrong. Credit to who is deserved for, and Apple deserved the credit for inventing Open CL, you have to admit it either you like Apple or not.
Apple has taken the industry of HPC upside down with Open CL, for the first time there is one single state of the art API and environment for high performance, multi-core and GPU programing, which is also OS and hardware independent. Open CL goes well beyond Direct X, as the latter is not only limited to what you can do for GPGPU, but also it is only designed for GPU (Microsoft is very late in the world of GPGPU, Apple has been targeting the GPU for high performance processing for a while now with Core Image and Core Video).
Open CL offers an unique interface for both CPU and GPU, which in other words means that it brings together different technologies like Open MP or CUDA, this is unique in the industry, Apple deserves the credit for having created this single interface.
Open CL is designed to target a large set of devices like CPU, GPU, Cell chips, DSPs, Direct X can't do that. Open CL targets small factor devices like the iPhone, Direct X does not and can not.
Not only the author of the article fails to recognize this unique aspect of Open CL, but he also fails to comment on the effort made by Apple in creating Open CL. Again you like Apple or not, that does not matter, give the credit to who it is deserved for and get the facts right.
Please correct the article and make it more interesting on what Open CL is really for, not the general bla, bla which is written.
Thanks.
ltcommanderdata - Thursday, January 1, 2009 - link
Which part isn't true? That Apple developed OpenCL and then submitted to Khronos? Since even Khronos admits that is true.http://www.khronos.org/news/press/releases/khronos...">http://www.khronos.org/news/press/relea...es_heter...
"Apple has proposed the Open Computing Language (OpenCL) specification to enable any application to tap into the vast gigaflops of GPU and CPU resources through an approachable C-based language."
Apple's Aaftab Munshi was also the chairman of the OpenCL working group.
And how is OpenCL late in the game? I'm pretty sure that DirectX 11 is the only standardized GPGPU implementation across multiple vendors, but it's still in beta. In comparison OpenCL has been ratified, in record time compared to OpenGL 3.0, probably due to Apple's pressure to get it ready for Snow Leopard. And nVidia has already released OpenCL drivers for Windows and Linux.
http://developer.nvidia.com/object/opengl_3_driver...">http://developer.nvidia.com/object/opengl_3_driver...
yyrkoon - Thursday, January 1, 2009 - link
Oh, and sorry, my original point was something like this. While the true innovative companies are squabbling about whose product is superior, Apple sneaks up behind them, and claims to have invented the internet. In other words, whether Apple participated or not, an open standard would have been made.melgross - Friday, January 2, 2009 - link
You're not very knowledgeable. You ARE very anti-Apple apparently.And why do gamers have to be the most beneficial parties? What's so great about gaming? Besides, OpenCL will benefit them, as well as parties that won't be benefitted by DirectX. Is that a bad thing? To you, it seems to be.
If MS had developed this, you would be jumping up and down, and claiming that it was the next step beyond the now old DirectX methodology, and far more useful.
Like it or not, this IS a major innovation, otherwise, so many companies of note wouldn't be signing on so quickly.
Whether Windows users benefit from this, or are left out of it is up to MS, who seems only interested in destroying standards that don't result in MS's increasing dominance. Too bad for them! That doesn't work too well anymore.
You know nothing about innovation at all. That's sad. Just go on being blinded by your prejudices, we all see it for what it is.