OpenCL 1.0: The Road to Pervasive GPU Computing
by Derek Wilson on December 31, 2008 6:40 PM EST- Posted in
- GPUs
Why is Parallel Computing Hard?
There are plenty of issues with parallel programming. Breaking up the problem is often the most important and complex step, especially when the parallelism is not obvious. As we are rooted in a world of sequential programming, conceptualizing the parallelization of tasks that lend themselves to sequential programming is tough. This can require not only the reworking of code, but redesigning the entire process of solving a problem.
Even in problems that lend themselves to parallelism, exploiting the parallelism can be tough. Even if you know the best and fastest algorithm for solving a data parallel problem, it isn't always possible to translate that to an efficient program. For instance, if I want to multiply two matrices with 100k x 100k dimentions, I can't just spawn all the threads I would need. If I were using POSIX threads to calculate one cell of the result matrix each, I would spend more time creating threads and allocating resources than actually doing the computation. I've got to take the resources I have and use them to the best of my ability. Though I can do matrix multiplication in parallel, I have to be careful about how I break up the problem and I can't exploit all the parallelism possible because of the tools I normally work with.
We are also limited in terms of hardware resources. With only a few processors available for general purpose programming, even if the software overhead weren't an issue we couldn't actually get any speed up from parallelizing beyond a certain point. This not only means that we can't exploit tons of parallelism even if the algorithm lends itself to it and this discourages programmers from thinking in terms of parallelism.
How Does OpenCL Help?
What if we had not only a pool of hardware resources hundreds wide that could handle thousands of threads in flight at a time with no software overhead? Well, we do: it's called a GPU. And if we could use the GPU for processing, then we could spawn a bunch of threads and really chew through the matrix multiplication we talked about earlier (or whatever). We might still have to be concerned about how many hardware resources we have in order to best map the problem to the specific device in the system. And we still have the problem of actually spawning, managing and running threads on the GPU hardware.
But what if we could write a special function, called a kernel, that can instantly be spawned hundreds or thousands or millions of times and run on different data all without needing to handle creating and managing all the threads ourselves. And what if we didn't need to worry about how to break up our problem and left actually determining how to handle allocating threads to the runtime? Well, now we have a solution: that's OpenCL.
The GPU is the vehicle for exploiting data parallelism. But before now our vehicle has run like a train on a track called real-time 3D graphics acceleration. OpenCL removes the track and the limitations and builds in a steering wheel developers can use to take the GPU (and other parallel devices) anywhere a programmer can imagine.
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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.