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Ask Slashdot: What Is the Most Painless Intro To GPU Programming? 198

dryriver writes "I am an intermediate-level programmer who works mostly in C# NET. I have a couple of image/video processing algorithms that are highly parallelizable — running them on a GPU instead of a CPU should result in a considerable speedup (anywhere from 10x times to perhaps 30x or 40x times speedup, depending on the quality of the implementation). Now here is my question: What, currently, is the most painless way to start playing with GPU programming? Do I have to learn CUDA/OpenCL — which seems a daunting task to me — or is there a simpler way? Perhaps a Visual Programming Language or 'VPL' that lets you connect boxes/nodes and access the GPU very simply? I should mention that I am on Windows, and that the GPU computing prototypes I want to build should be able to run on Windows. Surely there must a be a 'relatively painless' way out there, with which one can begin to learn how to harness the GPU?"
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Ask Slashdot: What Is the Most Painless Intro To GPU Programming?

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  • by Anonymous Coward

    I tried it out once a while ago just to see what it does. It looks 'dead' from a support POV, but it is still out there;

    Release notes for MC# 3.0:
    a) GPU support both for Windows and Linux,
    b) integration with Microsoft Visual Studio 2010,
    c) bunch of sample programs for running on GPU (including multi-GPU versions),
    d) "GPU programming with MC#" tutorial.

  • by Anonymous Coward on Friday July 19, 2013 @04:35PM (#44331929)

    GPU programming is painful. A painless introduction doesn't capture the flavor of it.

    • by PolygamousRanchKid ( 1290638 ) on Friday July 19, 2013 @05:07PM (#44332317)

      Yeah, it would be like S&M without the pain . . . cute, but something essential is missing from the experience.

      Heidi Klum has a TV show call "Germany's Next Top Model". She basically gets all "Ilsa, She-Wolf of the SS" on a bunch of neurotic, anorexic, pubescent girls, teaching them how a top model needs to suffer.

      Heidi Klum would make a good GPU programming instructor.

      . . . and even non-geeks would watch the show. A win-win for everyone.

  • Learn OpenCL (Score:5, Insightful)

    by Tough Love ( 215404 ) on Friday July 19, 2013 @04:37PM (#44331939)

    Since the whole point of GPU programming is efficiency, don't even think about VBing it. Or Pythoning it. Or whatever layer of a shiny crap might seem superficially appealing to you.

    Learn OpenCL and do the job properly.

    • Re:Learn OpenCL (Score:5, Interesting)

      by Tr3vin ( 1220548 ) on Friday July 19, 2013 @04:41PM (#44331987)

      Learn OpenCL and do the job properly.

      This. OpenCL is C based so it shouldn't be that hard to pick up. The efficient algorithms will be basically the same no matter what language or bindings you use.

      • Learn OpenCL and do the job properly.

        This. OpenCL is C based so it shouldn't be that hard to pick up. The efficient algorithms will be basically the same no matter what language or bindings you use.

        Well, the first thing is to understand parallel programming and what sort of things work well in a GPU. With that basic understanding, then OpenCL becomes a tool for doing that work. Starting with an OpenCL based "hello world" type application would then be the next step.

      • If you're learning this for your job, maybe you can persuade your boss to pay for an OpenCL course like this one [].
    • Yep. Some things are intrinsically hard. GPU programming is SIMD programming [], so you have to work with data parallelism. It helps a lot if you understand how the hardware works. This is where assembly language experience can be a big plus.

      There's no substitute for detailed knowledge. Outside of instruction level parallelism, there is no "magic bullet" for parallel programming. Your have to learn things.

    • don't even think about VBing it. Or Pythoning it.

      Awwwwww yisssssss... mothoafokin Assembly!

    • Re:Learn OpenCL (Score:5, Informative)

      by CadentOrange ( 2429626 ) on Friday July 19, 2013 @05:03PM (#44332277)
      What's wrong with a higher level language that interfaces with OpenCL? You're still writing OpenCL, you're just using Python for loading/storing datasets and initialisation. If you're starting out, something like PyOpenCL might be better as it'll allow you to focus on writing stuff in OpenCL.
      • Re: (Score:2, Informative)

        by Anonymous Coward

        The thing that is hard about gpu programming isn't getting code that works, its getting code that is fast. One of the most significant issues is how the data is arranged and accessed on the GPU. A big portion of this is going to be related to how the data is setup/transfered/accessed over PCIe from/to main memory.

        Basically, your going to want to access that data in a manner that is fairly low level on the cpu side as well. So, the advantages of phython/etc are nullified when you have some binary blob like f

    • by mcmonkey ( 96054 )

      Since the whole point of GPU programming is efficiency, don't even think about VBing it. Or Pythoning it. Or whatever layer of a shiny crap might seem superficially appealing to you.

      Learn OpenCL and do the job properly.

      "VBing?" "Pythoning?"

      Learn English and answer the question properly.

  • by Anonymous Coward

    CUDA is extremely easy to learn and use (if you know C and of course have an NVidia card) and is well worth the effort for some projects. Alternatively you could try skipping GPU programming and just using OpenMP which would still greatly improve performance if your not already multithreading.

    • Re: (Score:2, Insightful)

      by Anonymous Coward

      Never under any circumstances use cuda. We don't need anymore proprietary garbage floating around. Use opencl only.

      • If you don't care how long your programs take to solve a problem, avoid coding in cuda. If you want to keep your job, and your employer needs to run the app on nvidia cards as fast as possible, you're writing it in cuda.

    • Re:CUDA (Score:5, Informative)

      by UnknownSoldier ( 67820 ) on Friday July 19, 2013 @05:32PM (#44332635)

      Agreed 100% about CUDA and OpenMP! Already invented a new multi-core string searching algorithm and having a load of fun playing around with my GTX Titan combing CUDA + OpenMP. You can even do printf() from the GPU. :-)

      The most _painless_ way to learn CUDA is to install CUDA on a Linux (Ubuntu) box or Windows box. []

      On Linux, at the command line fire up 'nsight' open the CUDA SDK samples and start exploring! And by exploring I mean single-stepping through the code. The NSight IDE is pretty darn good considering it is free.

      Another really good doc is the CUDA C Programming Guide. []

      Oh and don't pay attention to the Intel Propaganda - there are numerous inaccuracies:
      Debunking the 100X GPU vs CPU Myth: An Evaluation of Throughput Computing on CPU and GPU []

  • by Anonymous Coward

    don't know what the status is on Windows, but for high-performance computing, OpenACC is an emerging standard, with support by Cray and PGI compilers.

  • by Anonymous Coward

    The heavy lifting has mostly already been done for you. [] There are CUDA wrappers out there that, with a few changes to your code, run it as close to optimally as possible using the card's cores. We had a Nvidia guy come by and give a talk just to show off how relatively painless it is (similar to OpenMPI, in my opinion). If you've got a couple extra people around consider reaching out to Nvidia to have someone show everyone a few of the options.

  • Obsidian (Score:5, Informative)

    by jbolden ( 176878 ) on Friday July 19, 2013 @04:51PM (#44332103) Homepage

    I get the impression that CUDA/OpenCL is still the best option. This thesis on Obsidian [] presents, a Haskell set of binding which might be easier and also covers the basics quite well. Haskell lends itself really well because the language inherently is designed for parallelism because of purity and out of order computation. That being said, I think Obsidian is a bit rough around the edges but if you are looking for a real alternative, this is one.

    • I've seen a few people mention Haskell, but no love for Erlang in here. Any particular reason?

      • Re:Obsidian (Score:5, Informative)

        by jbolden ( 176878 ) on Friday July 19, 2013 @09:55PM (#44334431) Homepage

        The big issue is that Haskell is lazy. Which means in particular the programmer by default doesn't determine order of execution. This makes Haskell a better counter example since order of execution is so key to so many languages.

        Erlang's type system is rather typical dynamic while Haskell has a Hindley–Milner type system which again shows off the plusses of functional better.

        Haskell has more of the most sophisticated ideas in computer science than any other language. It has become the standard for computer science in particular language and compiler research. So when an idea is "news" there is very likely an implementation of Haskell of that idea. Erlang's community is more practical and less cutting edge.

        Haskell is easier to program in.

  • Check out Max/MSP/Jitter [].

    As you describe, the interface is VPL - connecting boxes / nodes to access the GPU is one of the (many) things the program is capable of. Depending on what you're trying to, you may also find Gen [] useful for generating GLSL shaders within the Max environment (although you can use other shaders as well).

    I'm currently neck-deep in a few Jitter projects using custom shaders, etc., and while it's great for rapid prototyping, getting good frame-rates and production stable code out i
  • by Chris Mattern ( 191822 ) on Friday July 19, 2013 @04:52PM (#44332133)

    Anyone who tells you differently is selling you something.

  • by Arakageeta ( 671142 ) on Friday July 19, 2013 @04:53PM (#44332151)

    Check out the Udacity class on parallel programming. It's mostly CUDA (I believe it's taught by NVIDIA engineers): []

    CUDA is generally easier to program than OpenCL. Of course, CUDA only runs on NVIDIA GPUs though.

  • OpenACC (Score:5, Interesting)

    by SoftwareArtist ( 1472499 ) on Friday July 19, 2013 @04:53PM (#44332161)

    OpenACC [] is what you're looking for. It uses a directive based programming model similar to OpenMP, so you write ordinary looking code, then annotate it in ways that tell the compiler how to transform it into GPU code.

    You won't get as good performance as well written CUDA or OpenCL code, but it's much easier to learn. And once you get comfortable with it, you may find it easier to make the step from there into lower level programming.

    • It works in theory. In practice, unless you understand your code well, and the way compiler built the instructions well, and understood what these directives very well, you wont get any speed improvements. There are times when the over heads slow down the code and the simple minded implementation had brain dead locks, and you end up with slower code.

      We have come a long way since the days of assembly and assembly in another name Fortran. But the overheads of the higher level languages have been masked a lo

      • True, and this is even more true on GPUs than CPUs. They do a lot less to shield you from the low level details of how your code gets executed, so those details end up having a bigger impact on your performance. And to make it worse, those details change with every new hardware generation!

        But for a new user just getting into GPU programming, it's easier to learn those things in the context of a simple programming model like OpenACC than a complicated one like CUDA or OpenCL. That just forces them to deal

  • VB.NET background. Wanted to get into GPGPU to accelerate some of my more complicated math calculations. Tried CLOO (open source .net GPU wrappers) and couldn't get it to work, tried AMD's OPENCL dev gui, couldn't get it to work. Eventually found the answer in python. GPGPU in pyopencl is well-documented thanks to the bitcoiners, and from .net you can either run the python in a shell, or write a little python kernel to listen for, and process commands. Only catch is the opencl abilities are limited, and you
  • Like in all attemps at getting stuff faster, you should first wonder what kind of performance you are already getting out of CPU implementation. Provided you seem to believe it is actually possible to get performance out of a VB like langage, I assume that your base implementation heavily sucks.

    Putting stuff on a GPU has for only goal to make things faster but it is mostly difficult to write and non portable. Having a good CPU implementation might just be what you need. It also might be easier for you to wr

  • Take a look at C++ AMP []. It is a small language extension that lets you target the GPU using C++. The platform takes care of most of the mechanics of running code on the GPU. Also check out this blog post [] for links to tutorials and samples.

  • by elashish14 ( 1302231 ) <(moc.liamg) (ta) (4clacforp)> on Friday July 19, 2013 @05:05PM (#44332293)

    Coursera has some courses on GPU programming, like this one [], and what's nice about them pretty slow, and I'm assuming that they explain things well. Other online courses probably offer the same, and I think the video lectures would be helpful in understanding the concepts.

    • by jasax ( 1728312 )
      I took that course: []

      I also took a course from Udacity: [] but this one I didn't finish, I've done perhaps 30% of it (I already had finished Coursera's). One of these days I'll go there to close matters :-)

      The courses in Udacity are "always online", so anyone can register anytime and finish the course with his/hers own pace. Quizzes, exams and grading with certificate included have no fixed limits. On the other hand, the courses f
      • Having researched both, OpenCL is definitively better by far. Granted, CUDA has the native advantage, but that's not always going to be there, and I think most would agree that vendor tie-in is a Very Bad Thing (tm)

  • Try Intel's free OpenCV (Computer Vision) library, which includes GPU acceleration.

  • by Jthon ( 595383 ) on Friday July 19, 2013 @05:12PM (#44332381)

    So there's nothing really easy about GPU programming. You can look at C++ AMP from Microsoft, OpenMP or one of the other abstractions but you really need to understand how these massively parallel machines work. It's possible to write some perfectly valid code in any of these environments which will run SLOWER than on the CPU because you didn't understand fundamentally how GPUs excel at processing.

    Udacity currently has a fairly decent intro course on GPU programming at: []

    It's based around NVIDIA and CUDA but most of the concepts in the course can be applied to OpenCL or another GPU programming API with a little syntax translation. Also you can do everything for the course in your web-browser and you don't need an NVIDIA GPU to finish the course exercises.

    I'd suggest running through that and then deciding on what API you want to end up using.

  • by Anonymous Coward on Friday July 19, 2013 @05:28PM (#44332585)

    If you are going to program a GPU, and you are looking for performance gains, you MUST understand the hardware. In particular, you must understand the complicated memory architecture, you must understand the mechanisms for moving data from one memory system to another, and you must understand how your application and algorithm can be transformed into that model.

    There is no shortcut. There is no magic. There is only hardware.

    If you do not believe me, you can hunt up the various Nvidia papers walking you through (in painful detail-- link below) the process of writing a simple matrix transpose operation for CUDA. The difference between a naive and a good implementation, as shown in that paper, is huge.

    That said, once you understand the principles, CUDA is relatively easy to learn as an extension of C, and the Nvidia profiler, NVVP, is good at identifying some of the pitfalls for you so that you can fix them.

  • by John_The_Geek ( 1159117 ) on Friday July 19, 2013 @05:33PM (#44332637)

    I teach this stuff daily, and the huge advance over the past year has been the availability of OpenACC, and now OpenMP 4, compilers that allow you to use directives and offload much of the CUDA pain to the compiler.

    There is now a substantial base of successful codes that demonstrate that this really works efficiently (both development time and FLOPS). S3D runs at 15 PFLOPS on Titan using this and may well win the Gordon Bell prize this year. Less than 1% of lines of code modified there. NVIDIA has a whole web site devoted to use cases.

    I recommend you spend a day to learn it. There are regular online courses offered, and there is a morning session on it this Monday at XSEDE 13 if you are one of those HPC guys. A decent amount is available online as well.

    BTW, with AMD moving to Fusion, the last real supporter of OpenCL is gone. NVIDIA prefers OpenACC or CUDA and Intel prefers OpenMP 4 for MIC/Phi. So everyone officially supports it, but no one really puts any resources into it and you need that with how fast this hardware evolves.

    • OpenACC may be higher-level(easier to use), but it still generates CUDA/OpenCL code. Your wording sounded like "OpenCL support is gone." I want to correct you on that. OpenCL is the future and wraps CUDA also. If you code for CUDA, you can only target CUDA hardware. If you code for OpenCL, you can target not only AMD, but also CUDA hardware. That was the point of the OpenCL spec in the first place. OpenCL can also transparently take advantage of the local CPU cores. OPENCL has one drawback. OpenCL

    • John,

      While I have to defer to your position as being a teacher of these things, I have to question what you say.

      a) OpenCL was intended as an open access API to GPGPU techniques. Has something changed to channel people into vendor-specific approaches?

      b) What advantages do OpenACC and OpenMP 4 offer over previous techniques? Are these standards-based?

      c) Which GPGPU language (if any) can one target in the sure knowledge that it is future-proof? In which ways is this superior to OpenCL?

      These are genuine questio

  • The only painful thing you have to do is to decide how to increase threading in your code.
    • Yes. This.

      60 independent cores with general purpose instruction set on the same die with fast interconnect. If you need to pack some parallel speed on and do real work, using a GPU is pissing in the wind. An Intel Phi lets you get the job done.

      GPUs do certain things very well, but the odds of your problem mapping well to GPUs is slight.

    • by godrik ( 1287354 )

      I was one of the first phi user outside of intel (not in thefirst batch, but in the second one). And programming Phi can be quite painful as well. People always try to make you believe that perfoance is easy. But frankly, it is not. You need to understand how the architecture works and many people are not trained like that nowadays. Throwing a GPU or a Phi will only bring more problem.

      From what the OP says, it is not even clear he used all the processing power available on his CPU. And since he ties to get

  • by jones_supa ( 887896 ) on Friday July 19, 2013 @05:39PM (#44332693)
    You would probably see a multi-fold increase in performance by simply converting your project from C# to C++.
    • Possibly [], but there are a lot of tasks that only see about a doubling of speed. A C++ port is only likely to speed things up, while a GPU one is certain to. (Presuming the assumption about parallel execution is correct)

      • by godrik ( 1287354 )

        That's a buggy claim. There is nothing in GPUs that ensures you will get performance. Many algorithms are very difficult to write in GPUs. You have (essentially) no cache which make none trivial memory access slow. You have thread divergence issues which can kill your performance even if it contains significant parallelism. There is no interwarp synchronisation which is quite painful for fine synchronisation.

        Clearly the picture is more complicated than "parallel execution" => performance on GPU. If you h

  • by Anonymous Coward

    Closest to painless I know of is

    The GPU Maven Plugin compiles Java code with hand-selected Java kernels to CUDA that can run on NVIDIA GPUs of compatibility level 2.0 or higher. It encapsulates the build process so that GPU code is as easy to build with maven as ordinary Java code. The plugin relies on the NVidia CUDA SDK being installed which must be done separately.

  • I went with OpenSceneGraph.

    Long ago, I tried xlib only, because at that time Motif was the only higher layer available, and it was proprietary. It was horrible. xlib has been superceded by XCB, but I wouldn't use that, not with all the other options out there today. XCB is a very low level graphics library, for drawing lines and letters in 2D. 3D graphics can be done with that, but your code would have to have all the math to transform 3D representations in your data into 2D window coordinates for XCB

    • Gah, should have read the summary more carefully. I was talking about 3D graphics, not general programming on the GPU.
      • Whew, I was just about to launch into a tirade on how wrong you were! As it stands, I'm going to be a lot less tired than I'd thought I'd be!

  • I wouldn't call her advanced coursework easy, but a resource that belongs on this thread: []

    Mary Hall is a professor of Computer Science. Her recent work is related to compilers and parallel programming on GPUs. Her professional web page is something like an on-line open course, or the framework of one.
  • There isn't really a painless way. Like a lot of skills in life, the only way to learn is through pain, suffering and frustration. But it makes the prize all the much more enjoyable. You need to be experienced at regular, serial programming in C/C++, then mangle all of it to figure out how to program in parallel. I literally read the CUDA programming's guide 5 times. And I felt like I gained as much on the fifth time as I did the first time. And don't expect your debugger to save you -- if it's like i
  • ... to code it in COBOL for you.
  • OpenCL or CUDA is a real pain, and a lot to learn. But any modern Intel quad core processor can deliver 50 billion floating point operations per second if you treat it right.

    Use C or C++ with the Clang compiler (gcc will do fine as well probably) and vector extensions. Newer Intel processors have 256 bit vector registers, so you can define vector types with 32 8-bit integers, 16 16-bit integers, 8 32-bit integers or 8 single precision floating point numbers, or 4 double precision floating point numbers.
  • I've just started with opencl and love it, it's fast, easy, debuggable (codel) and -with stable drivers- not too much of a pain when it goes wrong.

    I've been writing hlsl, glsl and arb vertex shaders for years and to me, opencl kernels are basically the same thing (language and limitation wise). Convert some full screen graphics effects to opencl for a first example, then make it do other stuff (maybe with buffers instead of images).

    Once you're used to making/debugging kernels, start splitting code/algorithm

  • by dsouth ( 241949 )

    The easiest on-ramp to speeding up image/video processing is probably the npp library [] [] It has functionality and syntax similar to Intel's ipp library but uses an NVIDIA cuda-capable GPU to accelerate the operations.

    If you want to dig in deeper you could explore OpenACC [] [] OpenACC is a directives based approach to accelerator programming. You comment or mark up your code with OpenACC directives that provide addi

  • I took some parallel processing classes in the last couple of years as part of my Master's program. CUDA was one of those tricky little beasts that basically takes a few minutes to learn (assuming a rock solid C/C++ background) but a lifetime to master the nuances.

    We were building little throw-away matrix multiply programs - for which we were given horribly inefficient and barely functional source to start with. The challenge was to make it run as fast as possible, with extra credit going to the fastest i

    • by Skapare ( 16644 )

      You should already know how to do a matrix multiply by now, and not need someone else's source code. The task is to figure out how to partition the work most effectively for the GPU. Classic matrix multiply source code would be misleading at best.

      Or switch to an embarrassingly parallel project like Mandelbrot/Julia set calculation. Now the challenge is to make it do multi precision arithmetic so you can go deep.

    • by mpfife ( 655916 )
      | This runs counter to the level of abstraction that most CS majors are used to dealing with

      That's very unfortunate to hear. I know when I studied CS in the 90's, the foundation was always based on understanding the underlying hardware. My OS class focused on hardware interrupts, protected mode operation, cache and memory hierarchies. The whole basis for strategies and methods of making fast algorithms depends on knowing how the underlying hardware works.

      How can you call yourself a computer scientist

  • Simply don't go in the same sentence. You inherently need to know a lot about the underlying hardware and programming models to take advantage of that hardware - and none of that is easy. Best advice? Maybe use C# and start with a good sample tutorial. After that, you're going to learn a lot more about image algorithms/etc. That's why I can still make amazing amounts of money knowing how to program for GPU's.
  • by Anonymous Coward

    Writing GPU programs is hard. Not only do you have to learn a new sets of APIs, you also have to understand the underlying architecture to extract decent performance. It requires a different approach to problem solving that requires months if not years to develop.

    Fortunately you don't need to read the entire cuda programming guide to program on the GPU. There are several excellent libraries out there which hide the complexities of the GPU architecture. Since you are doing image processing, I would recommend

  • If you are an intermediate level programmer as you say then you can easily learn to use a new programming paradigm. There is a coursera course [] which is ok and should do for your purposes.

No extensible language will be universal. -- T. Cheatham