Text of OpenCL Peter Holvenstot. OpenCL Designed as an API and language specification Standards maintained...
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OpenCL Peter Holvenstot
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OpenCL Designed as an API and language specification Standards maintained by the Khronos group Currently 1.0, 1.1, and 1.2 Manufacturers release their own SDK and drivers Major backers: Apple, AMD/ATI, Intel
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OpenCL Alternative to CUDA Not limited to ATI GPUs Designed for heterogenous computing Executable on many devices, including CPUs, GPUs, DSPs, and FPGAs
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OpenCL Similar structure of host programs and kernels Set of compute devices is called a 'context' Kernels executed by 'processing elements' Kernels can be compiled at run-time or build-time
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OpenCL Task Parallelism many kernels running at once OpenCL 1.2 device can be partitioned down to single Compute Unit Built-in kernels for device-specific functionality
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Advantages Same code can be run on different devices Can also be run on NVIDIA GPUs! AMD/ATI attempting to integrate compute elements into other platforms (Accelerated Processing Units) Limited library of portable math routines Most common BLAST and FFT routines
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Performance
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Disadvantages No official implementation Vendors may meet specs or add restrictions Apple adds restrictions on group size Devices need appropriate settings to perform well Different capabilities different performance Solution: Tuning/load balancing framework
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Non-Optimized Performance
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Restrictions No recursion, variadics, or function pointer Cannot dynamically allocate memory from device No native variable-length arrays, double-precision Some can be worked around by extensions
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Terminology CUDA: Scalar Core Streaming Multiprocssr Warp PTX OpenCL: Stream Core Compute Unit Wavefront Intermediate Language
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Terminology CUDA: Host Memory Global/Device Memory Local Memory Constant Memory Shared Memory Registers OpenCL: Host Memory Global Memory Constant Memory Local Memory Private Memory
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Terminology CUDA: Grid Block Thread Thread ID Block Index Thread Index OpenCL: NDRange Work group Work item Global ID Block ID Local ID
