search - ArrayFire帧搜索算法崩溃

Question

我对 ArrayFire 和 CUDA 开发总体来说是个新手，在使用 Thrust 惨遭失败后，我几天前才开始使用 ArrayFire。我正在构建一个基于 ArrayFire 的算法，该算法应该在存储在设备内存中的数十万个 32x32 帧的数据库中搜索单个 32x32 像素帧。首先，我初始化一个矩阵，该矩阵具有 1024 + 1 像素作为行(我需要一个额外的像素来保留帧组 ID)和预定义数量(本例为 1000)的帧，按列索引。

如果我取消注释“pixels_uint32 = device_frame_ptr[pixel_group_idx];”，这是执行搜索的函数程序崩溃。该指针似乎是有效的，所以我不明白为什么会发生这种情况。也许对于以这种方式访问​​设备内存有一些我不知道的事情？

#include <iostream>
#include <stdio.h>
#include <sys/types.h>
#include <arrayfire.h>

#include "utils.h"

using namespace af;
using namespace std;

/////////////////////////// CUDA settings ////////////////////////////////
#define TEST_DEBUG false
#define MAX_NUMBER_OF_FRAMES  1000 // maximum (2499999 frames) X (1024 + 1 pixels per frame) x (2 bytes per pixel) = 5.124.997.950 bytes (~ 5GB)
#define BLOB_FINGERPRINT_SIZE 1024 //32x32

//percentage of macroblocks that should match: 0.9 means 90%
#define MACROBLOCK_COMPARISON_OVERALL_THRESHOLD 768 //1024 * 0.75
//////////////////////// End of CUDA settings ////////////////////////////

array search_frame(array d_db_vec) 
{
    try {
        uint number_of_uint32_for_frame = BLOB_FINGERPRINT_SIZE / 2;

        // create one-element array to hold the result of the computation
        array frame_found(1,MAX_NUMBER_OF_FRAMES, u32);
        frame_found = 0;

        gfor (array frame_idx, MAX_NUMBER_OF_FRAMES) {

            // get the blob id it's the last coloumn of the matrix
            array blob_id = d_db_vec(number_of_uint32_for_frame, frame_idx);  // addressing with (pixel_idx, frame_idx)

            // define some hardcoded pixel to search for             
            uint8_t searched_r = 0x0;
            uint8_t searched_g = 0x3F;
            uint8_t searched_b = 0x0;

            uint8_t b1 = 0;
            uint8_t g1 = 0;
            uint8_t r1 = 0;

            uint8_t b2 = 0;
            uint8_t g2 = 0;
            uint8_t r2 = 0;

            uint32_t sum1 = 0;
            uint32_t sum2 = 0;

            uint32_t *device_frame_ptr   = NULL;
            uint32_t pixels_uint32       = 0;            

            uint pixel_match_counter = 0;

            //uint pixel_match_counter = 0;
            array frame = d_db_vec(span, frame_idx);
            device_frame_ptr = frame.device<uint32_t>();

            for (uint pixel_group_idx = 0; pixel_group_idx < number_of_uint32_for_frame; pixel_group_idx++) {
                // test to see if the whole matrix is traversed 
                // d_db_vec(pixel_group_idx, frame_idx) = 0;

                /////////////////////////////// PROBLEMATIC CODE ///////////////////////////////////
                pixels_uint32 = 0x7E007E0;
                //pixels_uint32 = device_frame_ptr[pixel_group_idx]; //why does this crash the program?
                // if I uncomment the above line the program tries to copy the u32 frame into the pixels_uint32 variable
                // something goes wrong, since the pointer device_frame_ptr is not NULL and the elements should be there judging by the lines above
                ////////////////////////////////////////////////////////////////////////////////////

                // splitting the first pixel into its components
                b1 = (pixels_uint32 & 0xF8000000) >> 27;   //(input & 11111000000000000000000000000000)
                g1 = (pixels_uint32 & 0x07E00000) >> 21;   //(input & 00000111111000000000000000000000)
                r1 = (pixels_uint32 & 0x001F0000) >> 16;   //(input & 00000000000111110000000000000000)

                // splitting the second pixel into its components
                b2 = (pixels_uint32 & 0xF800) >> 11;       //(input & 00000000000000001111100000000000)
                g2 = (pixels_uint32 & 0x07E0) >> 5;        //(input & 00000000000000000000011111100000)
                r2 = (pixels_uint32 & 0x001F);             //(input & 00000000000000000000000000011111)

                // checking if they are a match
                sum1 = abs(searched_r - r1) + abs(searched_g - g1) + abs(searched_b - b1);
                sum2 = abs(searched_r - r2) + abs(searched_g - g2) + abs(searched_b - b2);

                // if they match, increment the local counter
                pixel_match_counter = (sum1 <= 16) ? pixel_match_counter + 1 : pixel_match_counter;
                pixel_match_counter = (sum2 <= 16) ? pixel_match_counter + 1 : pixel_match_counter;             
            }

            bool is_found = pixel_match_counter > MACROBLOCK_COMPARISON_OVERALL_THRESHOLD;  
            // write down if the frame is a match or not        
            frame_found(0,frame_idx) = is_found ? frame_found(0,frame_idx) : blob_id;
        }

       // test to see if the whole matrix is traversed - this has to print zeroes
    if (TEST_DEBUG)
            print(d_db_vec);

        // return the matches array
    return frame_found;

    } catch (af::exception& e) {
        fprintf(stderr, "%s\n", e.what());
        throw;
    }
}

// make 2 green pixels
uint32_t make_test_pixel_group() {
    uint32_t b1 = 0x0;        //11111000000000000000000000000000
    uint32_t g1 = 0x7E00000;  //00000111111000000000000000000000
    uint32_t r1 = 0x0;        //00000000000111110000000000000000

    uint32_t b2 = 0x0;        //00000000000000001111100000000000
    uint32_t g2 = 0x7E0;      //00000000000000000000011111100000
    uint32_t r2 = 0x0;        //00000000000000000000000000011111

    uint32_t green_pix = b1 | g1 | r1 | b2 | g2 | r2;

    return green_pix;
}

int main(int argc, char ** argv) 
{
    info();

    /////////////////////////////////////// CREATE THE DATABASE ///////////////////////////////////////
    uint number_of_uint32_for_frame = BLOB_FINGERPRINT_SIZE / 2;

    array d_db_vec(number_of_uint32_for_frame + 1,   // fingerprint size + 1 extra u32 for blob id
                   MAX_NUMBER_OF_FRAMES,             // number of frames
                   u32);                             // type of elements is 32-bit unsigned integer (unsigned) with the configuration RGBRGB (565565)

    if (TEST_DEBUG == true) {
        for (uint frame_idx = 0; frame_idx < MAX_NUMBER_OF_FRAMES; frame_idx++) {       
            for (uint pix_idx = 0; pix_idx < number_of_uint32_for_frame; pix_idx++) {
                d_db_vec(pix_idx, frame_idx) = make_test_pixel_group();  // fill everything with green :D
            }
        }
    } else {
        d_db_vec = rand(number_of_uint32_for_frame + 1, MAX_NUMBER_OF_FRAMES);
    }

    cout << "Setting blob ids. \n\n";
    for (uint frame_idx = 0; frame_idx < MAX_NUMBER_OF_FRAMES; frame_idx++) {
        // set the blob id to 123456
        d_db_vec(number_of_uint32_for_frame, frame_idx) = 123456;  // blob_id = 123456
    }

    if (TEST_DEBUG)
        print(d_db_vec);

    cout << "Done setting blob ids. \n\n";

    //////////////////////////////////// CREATE THE SEARCHED FRAME ///////////////////////////////////

    // to be done, for now we use the hardcoded values at line 37-39 to simulate the searched pixel:
    //37        uint8_t searched_r = 0x0;
    //38        uint8_t searched_g = 0x3F;
    //39        uint8_t searched_b = 0x0;

    ///////////////////////////////////////////// SEARCH /////////////////////////////////////////////    
    clock_t timer = startTimer();    
    for (int i = 0; i< 1000; i++) {
        array frame_found = search_frame(d_db_vec);

        if (TEST_DEBUG)
            print(frame_found);
    }
    stopTimer(timer);

    return 0;
}

这是控制台输出，其中注释了该行:

arrayfire/examples/helloworld$ ./helloworld

ArrayFire v1.9.1(64位Linux，版本9af23ea)

许可证:服务器 (27000@server.acceleyes.com)

CUDA工具包5.0，驱动程序304.54

GPU0 Tesla C2075，5376 MB，计算 2.0

内存使用量:5312 MB 可用空间(总共 5376 MB)

设置 blob ID。

已完成 Blob ID 设置。

时间:0.03秒。

<小时/>

这是控制台输出，其中该行未注释:

arrayfire/examples/helloworld$ ./helloworld

ArrayFire v1.9.1(64位Linux，版本9af23ea)

许可证:服务器 (27000@server.acceleyes.com)

CUDA工具包5.0，驱动程序304.54

GPU0 Tesla C2075，5376 MB，计算 2.0

内存使用量:5312 MB 可用空间(总共 5376 MB)

设置 blob ID。

已完成 Blob ID 设置。

段错误

<小时/>

预先感谢您对此问题的任何帮助。我确实尝试了一切，但没有成功。

Answer 1

免责声明:我是 arrayfire 的首席开发人员。我看到你有posted on AccelerEyes forums同样，但我在这里发帖是为了解决您的代码的一些常见问题。

1. 不要在 gfor 循环内使用 .device()、.host()、.scalar()。这将导致 GFOR 循环内部出现分歧，而 GFOR 并不是为此设计的。

2. 您无法索引设备指针。该指针指向GPU 上的位置。当你这样做时device_frame_ptr[pixel_group_idx]; ，系统正在CPU 上寻找等效位置。这就是您的段错误的原因。

3. 使用矢量化代码。例如，您不需要 gfor 的内部 for 循环。而不是做b1 = (pixels_uint32 & 0xF8000000) >> 27;在 for 循环中，您可以执行 array B1 = (frame & 0xF800000000) >> 27; 。即，您不是将数据传回 CPU 并使用 for 循环，而是在 GPU 内执行整个操作。

4. 不要在 GFOR 中使用 if-else 或三元运算符。这些再次导致分歧。例如，pixel_match_counter = sum(sum1 <= 16) + sum(sum2 < 16);和found(0, found_idx) = is_found * found(0, found_idx) + (1 - is_found) * blob_id .

我已经回答了您面临的具体问题。如果您有任何后续问题，请关注我们的论坛和/或我们的支持电子邮件。 Stackoverflow 适合提出特定问题，但不适用于调试整个程序。