CUarray allocation for surfaces

Byte-Welt - Projekte / Projects JCuda
1

Hi all, Marco,

We implemented our whole application based on the driver API. Now I was trying to allocate an array to which a surface can be bound using cuArrayCreate3D with the CUDA_ARRAY3D_DESCRIPTOR.flags set to CUDA_ARRAY3D_SURFACE_LDST. However this does not seem to be working (in contrary to the 4.2 reference manual, the JCuda-docu also says leave .flags @ 0)
So I wanted to mix some runtime api in there, to check if using JCuda.cudaMalloc3DArray(cudaArray, desc, extent, CUDA_ARRAY3D_SURFACE_LDST) might do the trick.

But how do I get my CUarray pointer to be a cudaArray?
From the reference guide:

The types CUarray and struct cudaArray  represent the same data type and may be used interchangeably by casting
the two types between each other.
In order to use a CUarray in a CUDA Runtime API function which takes a struct cudaArray , it is necessary to
explicitly cast the CUarray to a struct cudaArray .
In order to use a struct cudaArray  in a CUDA Driver API function which takes a CUarray, it is necessary to explicitly
cast the struct cudaArray  to a CUarray .

So a constructor like CUarray(cudaArray a) might do the trick. However, it would be even better if the initial problem would be solved and we could have surface-bindable CUarray’s.

Thanks in advance Marco, as always: awesome work :slight_smile:

2

Hello,

I’ll try to investigate this in more detail in the next days. Can you post a code snippet showing how you tried to do the allocation initially?

bye
Marco

3

My bad,

Everything works as it should through the Driver API. The flags are passed correctly to the CUDA side. I was simply passing the wrong CUarray to my method :o. Maybe just update the Javadoc of the .flags field (now: “Intended for future use”).

To obtain equivalent Driver and Runtime API mixing as in C, a way to transform a CUarray into a cudaArray would still be needed though (see quote in first post). But that’s not an important feature for me (sticking to the Driver API :)).

Cheers,
Keeth

4

Hi

Good to hear that, and thanks for this hint: I have updated the Documentation of the main classes (JCuda and JCudaDriver), but missed that flag in CUDA_ARRAY3D_DESCRIPTOR.

However, I’ll also consider the " CUarray(cudaArray a)" that you mentioned, although it is not necessary in this specific case, but since it should at least be possible according to the documentation.

bye
Marco