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81 lines
3.3 KiB
Markdown
81 lines
3.3 KiB
Markdown
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Device-Side Launch From NVVM IR
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===============================
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This document is for the programming language and compiler implementers who
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target NVVM IR and plan to support Dynamic Parallelism in their langauge.
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It provides the low-level details related to supporting kernel launches at
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the NVVM IR level.
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This document assumes the CUDA runtime is used. The method for device-side
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launch using the OpenCL runtime is similar but different.
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This document is written after the "Device-Side Launch from PTX"
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section from CUDA C Programming Guide
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(http://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#device-side-launch-from-ptx).
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Kernel Launch APIs
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------------------
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Device-side kernel launches can be implemented using the following two APIs
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in an NVVM IR program: cudaLaunchDevice() and cudaGetParameterBuffer().
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cudaLaunchDevice() launches the specified kernel with the parameter buffer
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that is obtained by calling cudaGetParameterBuffer() and filled with the
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parameters to the launched kernel. The parameter buffer can be NULL, i.e.,
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no need to invoke cudaGetParameterBuffer(), if the launched kernel does not
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take any parameters.
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cudaLaunchDevice
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----------------
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At the NVVM IR level, cudaLaunchDeviceV2() needs to be declared in the
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form shown below before it is used.
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; NVVM IR level declaration of cudaLaunchDeviceV2
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declare i32 @cudaLaunchDeviceV2(i8*, %struct.CUstream_st*)
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The CUDA-level declaration below is mapped to one of the aftorementioned NVVM
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IR level declarations and is found in the system header file
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cuda_device_runtime_api.h. The function is defined in the cudadevrt system
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library, which must be linked with a program in order to use device-side
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kernel launch functionality.
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extern __device__ __cudart_builtin__ cudaError_t CUDARTAPI
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cudaLaunchDeviceV2(void *parameterBuffer, cudaStream_t stream);
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The first parameter is a pointer to the parameter buffer, and the
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second parameter is the stream associated with the launch. The layout
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of the parameter buffer is explained in "Parameter Buffer Layout"
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below.
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cudaGetParameterBuffer
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----------------------
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cudaGetParameterBufferV2() needs to be declared at the NVVM IR level
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before it's used. The NVVM IR level declaration must be in the form
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given below:
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; NVVM IR level declaration of cudaGetParameterBufferV2
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declare i8* @cudaGetParameterBufferV2(i8*, %struct.dim3, %struct.dim3, i32)
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The following CUDA-level declaration of cudaGetParameterBufferV2() is
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mapped to the aforementioned NVVM IR level declaration:
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extern __device__ __cudart_builtin__ void * CUDARTAPI
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cudaGetParameterBufferV2(void *func, dim3 gridDimension,
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dim3 blockDimension,
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unsigned int sharedMemSize);
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The first parameter is a pointer to the kernel to be launched, and the
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other parameters specify the launch configuration, i.e., as grid
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dimension, block dimension, and shared memory size.
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Parameter Buffer Layout
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-----------------------
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Parameter reordering in the parameter buffer is prohibited, and each individual
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parameter placed in the parameter buffer is required to be aligned. That is,
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each parameter must be placed at the n-th byte in the parameter buffer, where n
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is the smallest multiple of the parameter size that is greater than the offset
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of the last byte taken by the preceding parameter. The maximum size of the
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parameter buffer is 4KB.
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