[[File:Out1.png|thumb|Maze 10x10]]
* '''Introduction:'''
The Maze program (by corzani@github) generates a maze image (of type PNG).
The following function creates the canvas of the Maze and initialize it by filling all the hexadecimal within each pixel. After the canvas is filled, the function calls the createImage function. Finally, the function write the result from the createImage function in a png file using the "lpng" extension.
void MazePng::toPng(unsigned int scale) {
12. In VS, go to menu Build -> Build Solution
*Kernel: *Sum up'''Analysis: '''
[[File:SPDiagram.PNG]]
The diagram shows that maze less than the size of 2,250,000 cells perform better in the serial code. However, if the there are more cells, the parallelized code has better performanceif there are more cells to process.
== PHASE 3 ==
* Optimize attempt We have tried to optimize the maze program. However, the result of optimization did not improve the speed of the program. In fact, it made the program slower than the parallelization but only a little bit faster than the serial. === Attempt 1 ===
Instead, we decided We tried to use share memory in optimize the maze program by removing some of the GPU if statements to improve reduce thread divergence, however the speed of attempt made the program. However, slower than the phase 2 version and only a little bit faster than the maze image does not showing correctlyserial version.
== Presentation == '''1. IntroductionNew Kernels:'''* MazeThe program generates a maze in png file. It takes 2 arguments: the height and the width of the maze. *Original Code: /* * MazePng.cpp * * Created on: 12 Jul 2013 * Author: yac */ #include "MazePng.h" #include <stdio.h> #include <stdlib.h> #include <string.h> const png_byte WALL = 0x00; const png_byte PATH = 0xFF; MazePng::MazePng(const unsigned int width, const unsigned int height) : AbstractMaze(width, height) { } MazePng::~MazePng() { } void MazePng::toPng(unsigned int scale) { png_byte color_type; png_byte bit_depth; png_structp png_ptr; png_infop info_ptr; png_bytep *row_pointers; int height, width; FILE *fp; width = (this->width * 2) + 1; height = (this->height * 2) + 1; color_type = PNG_COLOR_TYPE_RGB; bit_depth = 8; row_pointers = new png_bytep[height]; for (int i = 0; i < height; ++i) { row_pointers[i] = new png_byte[width * 3]; for (int j = 0; j < width * 3; j += 3) { row_pointers[i][j] = WALL; row_pointers[i][j + 1] = WALL; row_pointers[i][j + 2] = WALL; } } createImage(row_pointers, 0); fp = fopen("out.png", "wb"); png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); info_ptr = png_create_info_struct(png_ptr); png_init_io(png_ptr, fp); png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, color_type, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE); png_write_info(png_ptr, info_ptr); png_write_image(png_ptr, row_pointers); png_write_end(png_ptr, NULL); png_destroy_write_struct(&png_ptr, &info_ptr); for (int i = 0; i < height; ++i) { delete[] row_pointers[i]; } delete[] row_pointers; fcloseInitialize all pixels to black (fphex 000); } void inline MazePng::setPixel(png_bytep *row_pointers, unsigned int x, unsigned int y, png_byte type) { row_pointers[y][0 + 3 * x] = type; row_pointers[y][1 + 3 * x] = type; row_pointers[y][2 + 3 * x] = type; } void MazePng::createImage(png_bytep *row_pointers, unsigned int scale) { /* for (unsigned int x = 0; x < ((width * 2) + 1); ++x) { setPixel(row_pointers, x, 0, WALL); } */ if (start < width) { setPixel(row_pointers, start * 2 + 1, 0, PATH); } png_byte temp[2] = { 0 }; for (unsigned int y = 0; y < height; ++y) { setPixel(row_pointers, 0, (y * 2) + 1, WALL); for (unsigned int x = 0; x < width; ++x) { switch ((cells[(y * width) + x] & 0xC0) >> 6) { case 2: temp[0] = PATH; setPixel(row_pointers, 2 + (x * 2), (y * 2) + 1, temp[0]); break; case 1: temp[1] = PATH; setPixel(row_pointers, 1 + (x * 2), (y * 2) + 2, temp[1]); break; case 0: setPixel(row_pointers, 2 + (x * 2), (y * 2) + 1, temp[0]); setPixel(row_pointers, 1 + (x * 2), (y * 2) + 2, temp[1]); break; } setPixel(row_pointers, 1 + (x * 2), (y * 2) + 1, PATH); } } } * Analysis: '''Parallelizable?''' The program function named toPng() has a runtime of O(n^2); it takes up an average of 42% (min: 35%; max: 50%) of the program's execution time. for (int i = 0; i < height; ++i) { row_pointers[i] = new png_byte[width * 3]; for (int j = 0; j < width * 3; j += 3) { row_pointers[i][j] = WALL; row_pointers[i][j + 1] = WALL; row_pointers[i][j + 2] = WALL; } } '''2. Parallelize''' '''3. Optimize''' * New Kernel
__global__ void k_drawWalls(png_byte* rows, const short* cells, const int width, const int height, const int len, const int size) {
int i = blockIdx.x * blockDim.x + threadIdx.x;
}
// Set pixels to white according to the pattern the cell belongs to
__global__ void k_drawPaths(png_byte* rows, const short* cells, const int width, const int height, const int len) {
int i = blockIdx.x * blockDim.x + threadIdx.x;
}
Because there were too many else if condition in the old Kernel, we rewrite the Kernel to avoid divergent.'''Analysis:'''
[[File:SPODiagram.PNG]]
*Sum up: For this attempt, the kernel executes for each cell instead of for each byte (in phase 2); it is no longer processing more than 1 pixel in each cell for every thread, which may be the cause to the longer processing time. === Attempt 2 === **Still too many if statement We decided to use shared memory in the Kernel**Almost GPU to improve the speed of the program. However, the maze image does not show correctly: the same section paths were showing as randomly coloured pixels; the cause is due to the serialthreads setting only a part (1/3, 2/3) of a pixel's values to hexadecimal F.
