What is the difference between creating a buffer object with clCreateBuffer + CL_MEM_COPY_HOST_PTR vs. clCreateBuffer + clEnqueueWriteBuffer?

user_380038 0
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I have seen both versions in tutorials, but I could not find out, what their advantages and disadvantages are. Which one is the proper one?

cl_mem input = clCreateBuffer(context,CL_MEM_READ_ONLY,sizeof(float) * DATA_SIZE, NULL, NULL);
clEnqueueWriteBuffer(command_queue, input, CL_TRUE, 0, sizeof(float) * DATA_SIZE, inputdata, 0, NULL, NULL);

vs.

cl_mem input = clCreateBuffer(context,CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, ,sizeof(float) * DATA_SIZE, inputdata, NULL);

Thanks.

[Update]

I added CL_MEM_COPY_HOST_PTR, to the second example to make it correct.

opencl memory-management
5 Answers

One major difference that I've run into:

cl_mem input = clCreateBuffer(context,CL_MEM_READ_ONLY,sizeof(float) * DATA_SIZE, NULL, NULL); clEnqueueWriteBuffer(command_queue, input, CL_TRUE, 0, sizeof(float) * DATA_SIZE, inputdata, 0, NULL, NULL);

This first set of commands will create an empty buffer and enqueue a command in your command queue to fill the buffer.

cl_mem input = clCreateBuffer(context,CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, ,sizeof(float) * DATA_SIZE, inputdata, NULL)

This second command will create the buffer and fill it immediately. Note that there's no command queue in this argument list, so it uses the contents of input data as it is right now.

If you've already been running CL code and your source pointer is dependent upon a previous command in the command queue completing (e.g. an enqueued read of a prior output buffer), you definitely want to use the 1st method. If you try to create and fill the buffer in a single command, you'll end up with a race condition in which the buffer contents will not properly wait on the completion of your prior buffer read.

user_6144810
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