Task separation between cpu and gpu in CUDA - gpu

Question

I'm quite new to CUDA programming and need help to proceed.
Right now I'm working on CUDA project and I need to split a application between CPU and GPU and measure performance.
For ex, for a Matrix addition program with array size say 1000, I want to split the array into half and give the first half(500 jobs) to CPU and rest half(500 jobs) of it to GPU and combine the final output. I'm not quite sure how to go about it.
I saw in another link where they suggested to use thread pools and queue. I started to use pthreads to do the same but I was clueless how to use them when it comes to GPU part of the code as internally I have to invoke kernel. I actually created two pthreads one assuming for CPU and another for GPU
for (int i=0;i < NUMTHRDS; i++) {
pthread_create(&thds[i], &attr, decideFunc, (void*)i);
}
and decideFunc is as follows. When I executed, my pthread at times goes into CPU mode itself twice. I want to execute first half in CPU and second half in GPU and combine appropriately.
how can i do that?
void* decideFunc(void *arg) {
int id,first,last;
id = (long)arg;
first = id * TBSIZE/NUMTHRDS;
last = (id + 1) * TBSIZE/NUMTHRDS;
printf("id:%d\n\n",id);
if(id == 0){
printf("In CPU thread");
matrixAddCPU(first, last); //**Can i invoke another function here ?**
print_result(P, first, last); //P is array to store my result
}else{
printf("In GPU thread");
matrixAddGPU(first, last); //This dint seem to be correct
}
pthread_exit((void*)0);
}
and my matrixAddCPU()
void matrixAddCPU(int f, int l) {
printf("\nInvoked f:%d l:%d\n",f,l);
int row,col;
for(row=f;row<l;row++) {
for(col=f;col<l;col++) {
P[row*WIDTH+col] = N[row*WIDTH+col] + M[row*WIDTH+col];
printf("P[%d*%d+%d]:%f\t",row,WIDTH,col,P[row*WIDTH+col]);
}
printf("\n");
}
}
I couldn't find any tutorials that does this kind of operation. I don't want to use CUDA streams as I don't intend to create multiple kernels. All i wanted is to split simple application between CPU and GPU and watch their performance in a profiler tool.
Is using pthreads the right way to go ? If so, I would appreciate any further details/guidance or a tutorial that will help me.