parallelizing code using openmp - openmp

Question

The function below contains nested for loops. There are 3 of them. I have given the whole function below for easy understanding. I want to parallelize the code in the innermost for loop as it takes maximum CPU time. Then i can think about outer 2 for loops. I can see dependencies and internal inline functions in the innermost for loop . Can the innermost for loop be rewritten to enable parallelization using openmp pragmas. Please tell how. I am writing just the loop which i am interested in first and then the full function where this loop exists for referance.
Interested in parallelizing the loop mentioned below.
//* LOOP WHICH I WANT TO PARALLELIZE *//
for (y = 0; y < 4; y++)
{
refptr = PelYline_11 (ref_pic, abs_y++, abs_x, img_height, img_width);
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
}
The full function where this loop exists is below for referance.
/*!
***********************************************************************
* \brief
* Setup the fast search for an macroblock
***********************************************************************
*/
void SetupFastFullPelSearch (short ref, int list) // <-- reference frame parameter, list0 or 1
{
short pmv[2];
pel_t orig_blocks[256], *orgptr=orig_blocks, *refptr, *tem; // created pointer tem
int offset_x, offset_y, x, y, range_partly_outside, ref_x, ref_y, pos, abs_x, abs_y, bindex, blky;
int LineSadBlk0, LineSadBlk1, LineSadBlk2, LineSadBlk3;
int max_width, max_height;
int img_width, img_height;
StorablePicture *ref_picture;
pel_t *ref_pic;
int** block_sad = BlockSAD[list][ref][7];
int search_range = max_search_range[list][ref];
int max_pos = (2*search_range+1) * (2*search_range+1);
int list_offset = ((img->MbaffFrameFlag)&&(img->mb_data[img->current_mb_nr].mb_field))? img->current_mb_nr%2 ? 4 : 2 : 0;
int apply_weights = ( (active_pps->weighted_pred_flag && (img->type == P_SLICE || img->type == SP_SLICE)) ||
(active_pps->weighted_bipred_idc && (img->type == B_SLICE)));
ref_picture = listX[list+list_offset][ref];
//===== Use weighted Reference for ME ====
if (apply_weights && input->UseWeightedReferenceME)
ref_pic = ref_picture->imgY_11_w;
else
ref_pic = ref_picture->imgY_11;
max_width = ref_picture->size_x - 17;
max_height = ref_picture->size_y - 17;
img_width = ref_picture->size_x;
img_height = ref_picture->size_y;
//===== get search center: predictor of 16x16 block =====
SetMotionVectorPredictor (pmv, enc_picture->ref_idx, enc_picture->mv, ref, list, 0, 0, 16, 16);
search_center_x[list][ref] = pmv[0] / 4;
search_center_y[list][ref] = pmv[1] / 4;
if (!input->rdopt)
{
//--- correct center so that (0,0) vector is inside ---
search_center_x[list][ref] = max(-search_range, min(search_range, search_center_x[list][ref]));
search_center_y[list][ref] = max(-search_range, min(search_range, search_center_y[list][ref]));
}
search_center_x[list][ref] += img->opix_x;
search_center_y[list][ref] += img->opix_y;
offset_x = search_center_x[list][ref];
offset_y = search_center_y[list][ref];
//===== copy original block for fast access =====
for (y = img->opix_y; y < img->opix_y+16; y++)
for (x = img->opix_x; x < img->opix_x+16; x++)
*orgptr++ = imgY_org [y][x];
//===== check if whole search range is inside image =====
if (offset_x >= search_range && offset_x <= max_width - search_range &&
offset_y >= search_range && offset_y <= max_height - search_range )
{
range_partly_outside = 0; PelYline_11 = FastLine16Y_11;
}
else
{
range_partly_outside = 1;
}
//===== determine position of (0,0)-vector =====
if (!input->rdopt)
{
ref_x = img->opix_x - offset_x;
ref_y = img->opix_y - offset_y;
for (pos = 0; pos < max_pos; pos++)
{
if (ref_x == spiral_search_x[pos] &&
ref_y == spiral_search_y[pos])
{
pos_00[list][ref] = pos;
break;
}
}
}
//===== loop over search range (spiral search): get blockwise SAD =====
**// =====THIS IS THE PART WHERE NESTED FOR STARTS=====**
for (pos = 0; pos < max_pos; pos++) // OUTERMOST FOR LOOP
{
abs_y = offset_y + spiral_search_y[pos];
abs_x = offset_x + spiral_search_x[pos];
if (range_partly_outside)
{
if (abs_y >= 0 && abs_y <= max_height && abs_x >= 0 && abs_x <= max_width )
{
PelYline_11 = FastLine16Y_11;
}
else
{
PelYline_11 = UMVLine16Y_11;
}
}
orgptr = orig_blocks;
bindex = 0;
for (blky = 0; blky < 4; blky++) // SECOND FOR LOOP
{
LineSadBlk0 = LineSadBlk1 = LineSadBlk2 = LineSadBlk3 = 0;
for (y = 0; y < 4; y++) //INNERMOST FOR LOOP WHICH I WANT TO PARALLELIZE
{
refptr = PelYline_11 (ref_pic, abs_y++, abs_x, img_height, img_width);
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk0 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk1 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk2 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
LineSadBlk3 += byte_abs [*refptr++ - *orgptr++];
}
block_sad[bindex++][pos] = LineSadBlk0;
block_sad[bindex++][pos] = LineSadBlk1;
block_sad[bindex++][pos] = LineSadBlk2;
block_sad[bindex++][pos] = LineSadBlk3;
}
}
//===== combine SAD's for larger block types =====
SetupLargerBlocks (list, ref, max_pos);
//===== set flag marking that search setup have been done =====
search_setup_done[list][ref] = 1;
}
#endif // _FAST_FULL_ME_
I have rewitten the code to try to resolve dependencies in the innermost for loop ie the for(y=0;y<4;y++) and lot of LineSadBlk's. Please comment if it is wrong. I think the refptr and orgptr is sorted out by this and dependencies are resolved but LineSadBlk0,1,2,3 are still having dependencies as if we run the first and second iteration in parallel which value of LineSadBlk0,1,2,3 will be taken by the thread. How to resolve this please.
/*!
***********************************************************************
* \brief
* Setup the fast search for an macroblock
***********************************************************************
*/
void SetupFastFullPelSearch (short ref, int list) // <-- reference frame parameter, list0 or 1
{
short pmv[2];
pel_t orig_blocks[256];
//pel_t *orgptr, *refptr[4];
pel_t *orgptr[4],*refptr[4]; //defined by me new
int offset_x, offset_y, x, y, range_partly_outside, ref_x, ref_y, pos, abs_x, abs_y, bindex, blky;
int LineSadBlk0, LineSadBlk1, LineSadBlk2, LineSadBlk3;
int max_width, max_height;
int img_width, img_height;
StorablePicture *ref_picture;
pel_t *ref_pic;
int** block_sad = BlockSAD[list][ref][7];
int search_range = max_search_range[list][ref];
int max_pos = (2*search_range+1) * (2*search_range+1);
int list_offset = ((img->MbaffFrameFlag)&&(img->mb_data[img->current_mb_nr].mb_field))? img->current_mb_nr%2 ? 4 : 2 : 0;
int apply_weights = ( (active_pps->weighted_pred_flag && (img->type == P_SLICE || img->type == SP_SLICE)) ||
(active_pps->weighted_bipred_idc && (img->type == B_SLICE)));
ref_picture = listX[list+list_offset][ref];
//===== Use weighted Reference for ME ====
if (apply_weights && input->UseWeightedReferenceME)
ref_pic = ref_picture->imgY_11_w;
else
ref_pic = ref_picture->imgY_11;
max_width = ref_picture->size_x - 17;
max_height = ref_picture->size_y - 17;
img_width = ref_picture->size_x;
img_height = ref_picture->size_y;
//===== get search center: predictor of 16x16 block =====
SetMotionVectorPredictor (pmv, enc_picture->ref_idx, enc_picture->mv, ref, list, 0, 0, 16, 16); //call 1
search_center_x[list][ref] = pmv[0] / 4;
search_center_y[list][ref] = pmv[1] / 4;
if (!input->rdopt)
{
//--- correct center so that (0,0) vector is inside ---
search_center_x[list][ref] = max(-search_range, min(search_range, search_center_x[list][ref]));
search_center_y[list][ref] = max(-search_range, min(search_range, search_center_y[list][ref]));
}
search_center_x[list][ref] += img->opix_x;
search_center_y[list][ref] += img->opix_y;
offset_x = search_center_x[list][ref];
offset_y = search_center_y[list][ref];
// orgptr=orig_blocks;
orgptr[0]= orig_blocks //all org pointers defined orig blocks
orgptr[1]= orig_blocks;
orgptr[2]= orig_blocks;
orgptr[3]= orig_blocks;
//===== copy original block for fast access =====
for (y = img->opix_y; y < img->opix_y+16; y++)
for (x = img->opix_x; x < img->opix_x+16; x++)
{
//*orgptr++ = imgY_org [y][x];
*(orgptr[0])++ = imgY_org [y][x]; // img stored in all orgptr
*(orgptr[1])++ = imgY_org [y][x];
*(orgptr[2])++ = imgY_org [y][x];
*(orgptr[3])++ = imgY_org [y][x];
}
//===== check if whole search range is inside image =====
if (offset_x >= search_range && offset_x <= max_width - search_range &&
offset_y >= search_range && offset_y <= max_height - search_range )
{
range_partly_outside = 0; PelYline_11 = FastLine16Y_11; //search range is fully inside image
}
else
{
range_partly_outside //search range is partly outside image
}
//===== determine position of (0,0)-vector =====
if (!input->rdopt)
{
ref_x = img->opix_x - offset_x;
ref_y = img->opix_y - offset_y;
for (pos = 0; pos < max_pos; pos++)
{
if (ref_x == spiral_search_x[pos] &&
ref_y == spiral_search_y[pos])
{
pos_00[list][ref] = pos;
break;
}
}
}
//===== loop over search range (spiral search): get blockwise SAD =====
for (pos = 0; pos < max_pos; pos++)
{
abs_y = offset_y + spiral_search_y[pos];
abs_x = offset_x + spiral_search_x[pos];
if (range_partly_outside)
{
if (abs_y >= 0 && abs_y <= max_height &&
abs_x >= 0 && abs_x <= max_width )
{
PelYline_11 = FastLine16Y_11; //call 2
}
else
{
PelYline_11 = UMVLine16Y_11; //call 3
}
}
//orgptr=orig_blocks;
orgptr[0]=orig_blocks;
orgptr[1]=orgptr[0]+16;
orgptr[2]=orgptr[1]+16;
orgptr[3]=orgptr[2]+16;
bindex = 0;
for (blky = 0; blky < 4; blky++)
{
LineSadBlk0 = LineSadBlk1 = LineSadBlk2 = LineSadBlk3 = 0;
// i added the following to take refptr out of loop
refptr[0] = PelYline_11 (ref_pic, abs_y, abs_x, img_height, img_width); //call either 2 or 3
abs_y++;
refptr[1] = PelYline_11 (ref_pic, abs_y, abs_x, img_height, img_width); //call either 2 or 3
abs_y++;
refptr[2] = PelYline_11 (ref_pic, abs_y, abs_x, img_height, img_width); //call either 2 or 3
abs_y++;
refptr[3] = PelYline_11 (ref_pic, abs_y, abs_x, img_height, img_width); //call either 2 or 3
abs_y++;
omp_set_num_threads(4);
#pragma omp parallel for reduction(+:LineSadBlk0,LineSadBlk1,LineSadBlk2,LineSadBlk3)
for (y = 0; y < 4; y++)
{
{
LineSadBlk0 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk0 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk0 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk0 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
}
{
LineSadBlk1 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk1 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk1 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk1 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
}
{
LineSadBlk2 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk2 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk2 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk2 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
}
{
LineSadBlk3 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk3 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk3 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
LineSadBlk3 += byte_abs [*(refptr[y])++ - *(orgptr[y])++];
}
}
}
block_sad[bindex++][pos] = LineSadBlk0;
block_sad[bindex++][pos] = LineSadBlk1;
block_sad[bindex++][pos] = LineSadBlk2;
block_sad[bindex++][pos] = LineSadBlk3;
}
}
//===== combine SAD's for larger block types =====
SetupLargerBlocks (list, ref, max_pos); //call4
//===== set flag marking that search setup have been done =====
search_setup_done[list][ref] = 1;
}
#endif // _FAST_FULL_ME_