Question

I have a struct Primitive, which has the following definition:

typedef struct Primitive {
    float m[12];
    float invm[12];
    enum PrimitiveType type;
    int rayDensity;
    float util1;             
    float util2;                
} Primitive;

I pass an array of these structs to my kernel in a constant memory buffer:

__constant Primitive *objects;

As part of an optimization exercise I want to look at loading the structs into local memory, so my kernel has code to the likes of this:

__kernel void test(int n_objects, __constant Primitives *objects) {
    local Primitive pFrom, pTo;

    for(int i = 0; i < n_objects; i++) {
        pFrom = objects[i]; 
    }

}

When I run this I get a compilation error saying :

ptxas application ptx input, line 42; error: State space mismatch between instruction and address in instruction 'ld'

As an experiment I have tried first copying the struct to a private variable and then to the local variable as follows :

__kernel void test(int n_objects, __constant Primitives *objects) {
    Primitive pF, Pt;
    local Primitive pFrom, pTo;

    for(int i = 0; i < n_objects; i++) {
        pF = objects[i]
        pFrom = pF; 
    }

}

Which now compiles and runs however it seems like the object is not deeply copied into the local variable pFrom.

Please note that my code samples are purely samples and I have removed everything for the sake of brevity. Also my code works fine when I use the primitive structs directly from the constant global memory.

Does anyone know what I am missing here, surely its some basic fundamental to deep copying or OpenCL address spaces.

Answer 1

What you need is the async_work_group_copy function. You can wait for this async operation to finish using the wait_group_events function.

Hope this helps.