Const memory in OpenCL

Accelerated Computing CUDA CUDA Programming and Performance
1

Hi,

first of all i dont know this is the right forum, pardon me.

i have some confusion in const memory in opencl. As far as i know, my current hardware supports 64k of const memory which i understood as one cannot allocate >64K const memory for a kernel, and the kernel may fail if one tries to allocate more than that. So just to test that point i created a stand alone application (linux/opencl) to test that.

clGetDeviceInfo with CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE returned 65536 bytes

later i created two read only buffer as

cl_mem buffer1 = clCreateBuffer(ctx, CL_MEM_READ_ONLY, max_buffer,NULL,NULL); // max_buffer = 65536
cl_mem buffer2 = clCreateBuffer(ctx, CL_MEM_READ_ONLY, max_buffer,NULL,NULL); 

...

..

//set it as kernel args
err |= clSetKernelArg(kernel, 4, sizeof(cl_mem), &buffer1);
err |= clSetKernelArg(kernel, 5, sizeof(cl_mem), &buffer2);

...
// write some thing into the buffers
clEnqueueWriteBuffer(cmdQ, buffer1, CL_TRUE, 0, max_buffer, buffer, 0, NULL, NULL); 
// buffer is a char* array with max_buffer size and filled with 1
clEnqueueWriteBuffer(cmdQ, buffer2, CL_TRUE, 0, max_buffer, buffer, 0, NULL, NULL);

..
//execute kernel

kernel code accepts these params as __constant char* buffers and adds the two and writes to an output buffer.

my questions are

  1. How does the kernel accept two 64K buffer as const ?, does this overflow to global ? the opencl doc says that 64K is the max buffer size, which is not equal to max const memory size
  2. Is there any method by which we can make sure that the memory is indeed const.
  3. or am i missing something/doing wrong