On running the below code to find prime numbers , it gave the following benchmarks :
Device : CPU
Realtime : approx. 3 sec
Usertime : approx. 32 sec
Device : GPU
Realtime - approx. 37 sec
Usertime - approx. 32 sec
Why is the usertime returned by GPU not less than that of CPU and no optimization occurs?
#include <stdio.h>
#include <stdlib.h>
#include <CL/cl.h>
#include <time.h>
#define MAX_SOURCE_SIZE (0x10000000)
#define RNGE (100000)
int main()
{
cl_platform_id platform_id = NULL;
cl_device_id device_id = NULL;
cl_context context = NULL;
cl_command_queue command_queue = NULL;
cl_mem Amobj = NULL;
cl_mem Bmobj = NULL;
cl_mem Cmobj = NULL;
cl_program program = NULL;
cl_kernel kernel = NULL;
cl_uint ret_num_devices;
cl_uint ret_num_platforms;
cl_int ret;
clock_t time_i, time_f;
time_i = clock();
int i;
int j;
int *A;
int *B;
A = (int *) malloc( RNGE * sizeof(int) );
B = (int *) malloc( RNGE * sizeof(int) );
FILE *fp;
const char fileName[] = "chk_mod.cl";
size_t source_size;
char *source_str;
fp = fopen(fileName, "r");
if ( ! fp ) {
fprintf(stderr, "Failed to load kernel.
");
exit(1);
}
source_str = (char *) malloc(MAX_SOURCE_SIZE);
source_size = fread(source_str, 1, MAX_SOURCE_SIZE, fp);
fclose(fp);
for ( i=0; i < RNGE; i++ ) {
A[ i ] = i;
B[ i ] = A[i];
}
ret = clGetPlatformIDs(1, &platform_id, &ret_num_platforms);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot get platform id.
" );
return 1;
}
ret = clGetDeviceIDs(platform_id, CL_DEVICE_TYPE_GPU, 1, &device_id, &ret_num_devices);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot get device id.
" );
return 1;
}
context = clCreateContext(NULL, 1, &device_id, NULL, NULL, &ret);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot create context
" );
return 1;
}
command_queue = clCreateCommandQueue(context, device_id, 0, &ret);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot create command queue.
" );
return 1;
}
Amobj = clCreateBuffer(context, CL_MEM_READ_ONLY, RNGE*sizeof(int), NULL, &ret);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot create buffer A
" );
return 1;
}
Bmobj = clCreateBuffer(context, CL_MEM_READ_WRITE, RNGE*sizeof(int), NULL, &ret);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot create buffer B
" );
return 1;
}
ret = clEnqueueWriteBuffer(command_queue, Amobj, CL_TRUE, 0, RNGE*sizeof(int), A, 0, NULL, NULL);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot enqueue in write buffer.
" );
return 1;
}
ret = clEnqueueWriteBuffer(command_queue, Bmobj, CL_TRUE, 0, RNGE*sizeof(int), B, 0, NULL, NULL);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot enqueue in write buffer.
" );
return 1;
}
program = clCreateProgramWithSource(context, 1, (const char **)&source_str, (const size_t *)&source_size, &ret);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot create program with source
" );
return 1;
}
ret = clBuildProgram(program, 1, &device_id, NULL, NULL, NULL);
kernel = clCreateKernel(program, "data_parallel", &ret);
if( ret != CL_SUCCESS ) {
printf( "Error : Cannot create kernel
" );
return 1;
}
ret = clSetKernelArg(kernel, 0, sizeof(cl_mem), (void *) &Amobj);
ret = clSetKernelArg(kernel, 1, sizeof(cl_mem), (void *) &Bmobj);
size_t global_item_size = RNGE;
size_t local_item_size = 1;
ret = clEnqueueNDRangeKernel(command_queue, kernel, 1, 0, &global_item_size, &local_item_size, 0, 0, 0 );
ret = clEnqueueReadBuffer(command_queue, Bmobj, CL_TRUE, 0, RNGE*sizeof(int), B, 0, NULL, NULL);
printf("Result: ");
for ( i=2; i < RNGE; i++ ) {
if ( B[i] ) {
printf( "%d ", B[i] );
}
}
printf("
");
ret = clFlush(command_queue);
ret = clFinish(command_queue);
ret = clReleaseKernel(kernel);
ret = clReleaseProgram(program);
ret = clReleaseMemObject(Amobj);
ret = clReleaseMemObject(Bmobj);
ret = clReleaseCommandQueue(command_queue);
ret = clReleaseContext(context);
free(source_str);
free(A);
free(B);
time_f = clock();
printf("Time elapsed = %7.3fs
", (float) (time_f - time_i)/CLOCKS_PER_SEC);
return 0;
}
Kernel file(chk_mod.cl) is:
Code:
__kernel void data_parallel( __global int *A, __global int *B )
{
int t;
int i = get_global_id(0);
for ( t = 2; t < i; t++ ) {
if ( i % t == 0 ) {
B[ i ] = 0;
}
}
}
System specifications :64-bit CentOS 5.3 system with two ATI Radeon 5970 graphics card + Intel Core i7 processor(12 cores)