AMD Radeon RX570 OpenCL内核数组参数传递失败问题排查

Let's walk through the problems in your code and fix them step by step:

1. Incorrect Pointer Handling in the Kernel #

Your Python code passes arg as a 2-element uint64 array, which maps to the kernel's __global const long * arg parameter. But in the kernel, you're incorrectly treating arg[0] and arg[1] as pointers:

ulong * number = (ulong *)arg[0];
ulong * prime_array_len = (ulong *)arg[1];

This is wrong—arg[0] is directly the value of your input number, and arg[1] is the length of the prime array. You don't need to cast them to pointers; just assign them directly to variables:

ulong number = arg[0];
ulong prime_array_len = arg[1];

2. Mismatched Data Types #

Type consistency is critical in OpenCL—mismatches cause undefined behavior (like the incorrect prime_array_len 0 output you're seeing):

• Your Python code uses np.uint64 for prime_number and res, but the kernel declares prime_array as __global long * and res as __global int *. These need to match. Change the kernel's parameter types to __global ulong * for both.
• The printf statement uses %d (for ints) to print ulong values. Use %lu instead to match unsigned long integers, which fixes the wrong length output.
• Inside the loop, long prime = prime_array[iter]; should be ulong prime to match the array's type.

3. Simplify Result Retrieval (Optional but Cleaner) #

While your enqueue_map_buffer works, using cl.enqueue_copy to pull the result back to the host is often more straightforward and less error-prone.

Fixed Kernel Code (is_prime.cl) #

__kernel void is_prime(
    __global const ulong * arg,
    __global ulong * prime_array,
    __global ulong * res
) {
    ulong number = arg[0];
    ulong prime_array_len = arg[1];
    ulong ret = 1;
    ulong iter = 0;

    printf("number = %lu prime_array_len %lu\n", number, prime_array_len);

    for (iter = 0; iter < prime_array_len; iter++) {
        ulong prime = prime_array[iter];
        if (prime * prime > number) {
            break;
        }
        if (number % prime == 0) {
            ret = 0;
            break;
        }
    }

    *res = ret;
}

Updated Python Code (Result Retrieval Section) #

Replace the map buffer code with this simpler copy operation:

cl.enqueue_copy(cl_queue, res, res_buffer)
return res[0]

After making these changes, running your code will output:

[3 1]
number = 3 prime_array_len 1

And the function will correctly return 1 (indicating 3 is prime), which is what you expect.

内容的提问来源于stack exchange，提问作者Silver