Hi!
I'm having synchronization problems with enqueueCopyBuffer() and Xeon PHI. Suppose the following pseudocode:
/* Begin host code */
cl::Buffer b0, b1; ///initialize with size N
cl::CommandQueue c0, c1;
cl::Kernel k;
char hB; ///initialize hB to 5
c0.enqueueWriteBuffer(b0, CL_TRUE, 0, N, static_cast<void *> (hB));
c0.enqueueNDRangeKernel(k, cl::NullRange, 1, 1); //one only thread
c1.enqueueCopyBuffer(b0, b1, 0, 0, N);
c1.enqueueReadBuffer(b1, CL_TRUE, 0, N static_cast<void *> (hB));
/*End host code */
/* The kernel code would be: */
__kernel void add1(__global char *p, int n) {
for(int i = get_global_id(0); i < n; i += 1)
p++;
}
The cuestion is: After the enqueueReadBuffer call, What values are stored in hB? The answer is 'it depends'. With two Nvidia GPUs the values are 6 and with two Xeon PHI are 5. The problem is that the implementation of the enqueueCopyBuffer in the Xeon Phi is non-blocking and it needs an synchronization barrier between the enqueueNDRangeKernel call and the enqueueCopyBuffer. Is this a normal behavior or it is an implementation error?
Thanks a lot in advance and good luck :)
Moisés
