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I am speaking out of ignorance, but my understanding is that modern graphics pipelines consist of software "shader" programs running on the GPGPU hardware. The

I am speaking out of ignorance, but my understanding is that modern graphics pipelines consist of software "shader" programs running on the GPGPU hardware. The GPU makers aren't including vast numbers of compute cores just as a bonus feature, they're how the graphics part works. Each little core runs the same shader program to render its set of pixels, reading and writing out to different offsets in shared memory buffers. The "general purpose" use basically boils down to writing a shader program that does useful math rather than draw pretty pictures.

namibj 7y ago
There is fixed hardware for 5 main purposes. 1. Output framebuffer. 2. Polygon rasterization (often limited to points and triangles). 3. Texture sampling. This is accessible in CUDA (I have ~zero experience with other GPGPU systems). 4. Afaik also for blending. This might have stopped now. 5. Video codecs (MPEG-2, H.263, H.264, H.265, VP8, VP9, soon AV1) decoding, and also encoding for some of them. Nvidia RTX also include ray tracing hardware that handles that task more efficienly (I presume by using fixed logic for dispatching memory/cache-aware computations like e.g. content-addressable memory and such). Most things are handled by the shader cores. They are 1024bit SIMD with lane-masking until Volta, and a more flexible/arbitrary fork/join since Turing (not all Turing has the ray tracing hardware), which also brought a scalar execution port with it (like amd64 getting traditional RAX/RDX/etc. with their opcodes after only having AVX instructions). AMD GCN afaik has a quite explicit SIMD architecture, with a scalar execution port since inception. Also 1024bit iirc.
- fizixer 7y ago
  Hey thanks for the very useful reply. Now that you mention, could you point to any reading resource for getting into the nitty gritty of the fixed hardware part of the GPU? From my interactions with some folks, I'm under the impression that this stuff is kept proprietary and both nVidia and AMD don't reveal the details. I'm just wondering if there are some general principles related to the fixed hardware aspect of the graphics pipeline of a GPU, that are compiled in a text or review paper or something. Thanks in advance.

namibj 7y ago

There is fixed hardware for 5 main purposes. 1. Output framebuffer. 2. Polygon rasterization (often limited to points and triangles). 3. Texture sampling. This is accessible in CUDA (I have ~zero experience with other GPGPU systems). 4. Afaik also for blending. This might have stopped now. 5. Video codecs (MPEG-2, H.263, H.264, H.265, VP8, VP9, soon AV1) decoding, and also encoding for some of them. Nvidia RTX also include ray tracing hardware that handles that task more efficienly (I presume by using fixed logic for dispatching memory/cache-aware computations like e.g. content-addressable memory and such). Most things are handled by the shader cores. They are 1024bit SIMD with lane-masking until Volta, and a more flexible/arbitrary fork/join since Turing (not all Turing has the ray tracing hardware), which also brought a scalar execution port with it (like amd64 getting traditional RAX/RDX/etc. with their opcodes after only having AVX instructions). AMD GCN afaik has a quite explicit SIMD architecture, with a scalar execution port since inception. Also 1024bit iirc.

fizixer 7y ago
Hey thanks for the very useful reply. Now that you mention, could you point to any reading resource for getting into the nitty gritty of the fixed hardware part of the GPU? From my interactions with some folks, I'm under the impression that this stuff is kept proprietary and both nVidia and AMD don't reveal the details. I'm just wondering if there are some general principles related to the fixed hardware aspect of the graphics pipeline of a GPU, that are compiled in a text or review paper or something. Thanks in advance.