cuda - cudaMemcpyToSymbol vs. cudaMemcpy why is it still around (cudaMemcpyToSymbol)

Question

As stated by other questions and according to the link, you can no longer use the symbol name for this function. Now that the feature is gone, when would ever want to use this over cudaMemCpy? When would you ever want to use it at all? What is the tradeoff or benefit?

https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__MEMORY.html#group__CUDART__MEMORY_1g9bcf02b53644eee2bef9983d807084c7

Answer 1

In short, because cudaMemcpy can't do the same thing as cudaMemcpyToSymbol without an additional API call. Consider a constant memory array:

__constant__ float coeffs[8];

To copy values to this array using cudaMemcpyToSymbol, just do

cudaMemcpyToSymbol(coeffs, hostData, 8*sizeof(float));

To do the same with cudaMemcpy requires this:

float *dcoeffs;
cudaGetSymbolAddress((void **)&dcoeffs, coeffs);
cudaMemcpy(dcoeffs, hostData, 8*sizeof(float), cudaMemcpyHostToDevice);

A direct call to cudaMemcpy is illegal without prior symbol lookup.

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