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[[Category:Tutorials|GPU Computing (CUDA C)]]<nowiki /> {{DISPLAYTITLE:GPU Computing (CUDA C)}}<nowiki /> {{Syllabus Introduction to GPU Computing}}<nowiki /> __TOC__ This video discusses the SAXPY via NVIDIA CUDA C/C++. CUDA is an application programming interface (API) for NVIDIA GPUs. In general, CUDA works with many programming languages, but this tutorial is going to focus on C/C++. CUDA gives access to a GPUs instruction set, which means we have to go through everything step-by-step, since many things do not happen automatically. === Video === <!--T:5--> <youtube width="600" height="340" right>rgqORzT1oCw</youtube> ([[Media:GPU_tutorial_saxpy_cuda_c.pdf |Slides as pdf]]) === Quiz === <!--T:5--> {{hidden begin |title = 1. Which features does CUDA add to C/C++?}} <quiz display=simple> { |type="()"} - new functions || CUDA does not only add new functions, but all of these features. - new syntax || CUDA does not only add new syntax, but all of these features. - GPU support || CUDA does not only add GPU support, but all of these features. + All of the above || Correct </quiz> {{hidden end}} {{hidden begin |title = 2. What is a kernel?}} <quiz display=simple> { |type="()"} - It's a flag you can set to automatically parallelize any function. || Unfortunately, life is not that easy. + It's the part of your code that is run on the GPU. || Correct - It's a new CUDA function that activates the GPU. || Wrong </quiz> {{hidden end}} {{hidden begin |title = 3. How do you flag a function to be a kernel?}} <quiz display=simple> { |type="()"} - __host__ || Wrong. This specifies a function that runs on the CPU. - __device__ || Wrong. This indeed does specify a function that runs on the GPU, but it also needs to be called from the GPU, while we want a kernel to be launched by the CPU. + __global__ || Correct - __GPU__ || Wrong. This modifier doesn't exist. </quiz> {{hidden end}} {{hidden begin |title = 4. Let's say you coded your kernel function called "MyKernel". How do you run it?}} <quiz display=simple> { |type="()"} - MyKernel(); || Wrong. This would just execute an ordinary function. - CUDA.run(NoBlocks, NoThreads, MyKernel()); || Wrong. There is no CUDA.run() + <<<NoBlocks, NoThreads>>>MyKernel(); || Correct - __global(NoBlocks, NoThreads)__ MyKernel(); || Wrong. __global__ and other modifiers cant have arguments and are part of a function definition, not launch. </quiz> {{hidden end}} {{hidden begin |title = 5. Inside your kernel function, how do you distribute your data over the GPU threads?}} <quiz display=simple> { |type="()"} - You don't have to, CUDA does that automatically for you. || Wrong + Each thread has has an index attached to it, which is addressed via threadIdx.x || Correct - If you use array-element-wise operations, e.g.: y.=a.*x.+b . This is managed by the NVIDIA preprocessor. || Wrong. There are no element-wise operators in C/C++ - You flag a line to be parallelized via keywords, e.g.: __device__ y=a*x+b || Wrong. These modifiers are used at function definitions. </quiz> {{hidden end}}

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