![]() ![]() ![]() ![]() Error with gcc but not with clang when compiling initializer list containing pointers to template function.Do we still need to write the empty angle brackets when using transparent std function objects?.Using std::move() when returning a value from a function to avoid to copy.What's the syntax for declaring an array of function pointers without using a separate typedef?.When doing Function Pointers what is the purpose of using the address-of operator vs not using it?.CUDA launches host function as kernel when using function pointers.I would strongly recommend not trying to rely on this behaviour. So the language specification requirements are skipped and things accidentally work. The code which is produced happens to work with either a host function or a host kernel wrapper function because the runtime support code doesn't (and probably can't) emit code which could perform introspection on the function pointer and identify that the function pointer isn't going to call a kernel. The reason why Copy>(d_input, d_output) ĭoesn't compile, is because Copy is a host function and nvcc can detect that at compile time - in the language specification only _global_ functions can launched and the compiler enforces this check.īut when you pass a function pointer, the compiler cannot apply that check. Technically, it is undefined behaviour, because the way that kernel launches work internally inside the CUDA runtime API are deliberately opaque and implementation details might change over time. This is how you can provide either CopyKernel or Copy as a argument to TestFunctionPointerLaunch and it will still work. Copy), then that host code will do the same thing, and a kernel launch will eventually result, just further down the call stack. If f happens to be a host function which itself contains a runtime API kernel call (ie. CopyKernel), then a kernel launch will result via the API calls which the wrapper contains, otherwise it won't. If f happened to be a kernel wrapper function (ie. launch parameters for a kernel launch are pushed onto the driver, and the host function supplied as f is called. Is compiled to this by the CUDA front end preprocessor (cudaConfigureCall(1, 32)) ? (void)0 : f(d_input, d_output) ![]() So what happens in TestFunctionPointerLaunch? Basically the same thing. the kernel launch configuration is pushed to the driver, and then the wrapper function is called, where the arguments are pushed to the driver and the kernel launched. Instead, whenever a CopyKernel>() call is encountered by the preprocessor, this sort of code is emitted: (cudaConfigureCall(1, 32)) ? (void)0 : (CopyKernel)(d_input, d_output) You will notice that the execution configuration for the kernel is not handled within these functions. These provide a wrapper around the necessary API calls to push the kernel arguments to the CUDA driver and launch the kernel. _device_stub_Z10CopyKernelPKiPi( _cuda_0,_cuda_1) Void CopyKernel( const int *_cuda_0,int *_cuda_1) (void)cudaLaunch(((char *)((void ( *)(const int *, int *))CopyKernel))) If (cudaSetupArgument((void *)(char *)&_par1, sizeof(_par1), (size_t)8Ui64) != cudaSuccess) return If (cudaSetupArgument((void *)(char *)&_par0, sizeof(_par0), (size_t)0Ui64) != cudaSuccess) return When the nvcc compiles your CopyKernel and a runtime API style launch for that kernel, a pair of host functions get emitted which looks like this: void _device_stub_Z10CopyKernelPKiPi(const int *_par0, int *_par1) The first insight required is to demystify how kernels are compiled and how their launches actually work in the CUDA runtime API. The CopyKernel is being called three times on the device, but all of the launches are being initiation on the host. I can see why this might be a bit confusing, but despite what you might think is happening Copy is never running on the GPU. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |