openmp

For-loop inside parallel region

由 |▌冷眼眸甩不掉的悲伤 提交于 2020-01-04 06:25:09
问题 If there is a for-loop inside a parallel region, would for-loop be parallelized again or every thread will execute its own for-loop? T sum; #pragma omp parallel { #pragma omp for reduction(+: sum) for (;;) { T priv_var; sum += priv_var; } } 回答1: Yes, this code will cause OpenMP to parallelise the for loop across the threads that are spawned by the parallel region. However, I believe that your current for statement is invalid for OpenMP parallelisation. You need to explicitly provide an

What happens in OpenMP when there's a pragma for inside a pragma for?

由 只愿长相守 提交于 2020-01-04 06:01:11
问题 At the start of #pragma omp parallel a bunch of threads are created, then when we get to #pragma omp for the workload is distributed. What happens if this for loop has a for loop inside it, and I place a #pragma omp for before it as well? Does each thread create new threads? If not, which threads are assigned this task? What exactly happens in this situation? 回答1: By default, no threads are spawned for the inner loop. It is done sequentially using the thread that reaches it. This is because

What happens in OpenMP when there's a pragma for inside a pragma for?

由 半城伤御伤魂 提交于 2020-01-04 06:01:08
问题 At the start of #pragma omp parallel a bunch of threads are created, then when we get to #pragma omp for the workload is distributed. What happens if this for loop has a for loop inside it, and I place a #pragma omp for before it as well? Does each thread create new threads? If not, which threads are assigned this task? What exactly happens in this situation? 回答1: By default, no threads are spawned for the inner loop. It is done sequentially using the thread that reaches it. This is because

GPU---并行计算利器

由 笑着哭i 提交于 2020-01-04 05:06:09
大数据集群计算利器之MPI/OpenMP ---以连通域标记算法并行化为例 1 背景 图像连通域标记算法是从一幅栅格图像（通常为二值图像）中，将互相邻接（4邻接或8邻接）的具有非背景值的像素集合提取出来，为不同的连通域填入数字标记，并且统计连通域的数目。通过对栅格图像中进行连通域标记，可用于静态地分析各连通域斑块的分布，或动态地分析这些斑块随时间的集聚或离散，是图像处理非常基础的算法。目前常用的连通域标记算法有1）扫描法（二次扫描法、单向反复扫描法等）、2）线标记法、3）区域增长法。二次扫描法由于简单通用而被广泛使用！ 图1 连通域标记示意图 随着所要处理的数据量越来越大，使用传统的串行计算技术的连通域标记算法运行时间过长，难以满足实际应用的效率需求。随着并行计算技术的发展，利用不同的编程模型，许多数据密集型的计算任务可以被同时分配给单机多核或多机多处理器进行并行处理，从而有可能大幅度缩减计算时间。目前在集群计算领域广泛使用MPI来进行并行化，在单机领域广泛使用OpenMP进行化，本文针对基于等价对的二值图像连通域标记算法的进行了并行化设计，利用不同的并行编程模型分别实现了不同的并行算法，并通过实验对利用不同并行编程模型所实现的连通域标记算法进行了性能对比分析。 2 二次扫描串行算法思想 　　 顾名思义，二次扫描串行算法步骤包含两部分。 2.1 第一次扫描 a）标记 b

Is there a way that OpenMP can operate on Qt spanwed threads?

由 牧云@^-^@ 提交于 2020-01-04 04:00:44
问题 I'm trying to parallelize a number-crunching part of an application to make use of a quad-core architecture using OpenMP and GCC 4.2 on Mac OS 10.5. But what I think the problem is that this application uses Qt for the GUI and I'm trying to fork the worker threads on a secondary thread created by Qt which causes the program to crash - but of this I'm not sure. I'm seriously on the dark here since it's my first time working with either Qt or OpenMP, (or C++ for that matter). Any sort of

How to implement OpenMP multiple level code using C# Parallel.For

由 自闭症网瘾萝莉.ら 提交于 2020-01-03 19:34:34
问题 How to implement in following OpenMP code using C# Parallel.For OpenMP Code #pragma omp parallel { float[] data = new float[1000]; #pragma omp for for(int i = 0; i < 500; i++) { for(int j = 0; j < 1000; j++) { data[j] =100; // do some computation using data } } } I also tried the following but it was not exactly what OpenMP code did. In the openMP code, it was allocating Memory per thread and performs the nested loop computation. Whereas the code below, actually allocates memory for each i,

How to implement OpenMP multiple level code using C# Parallel.For

由 淺唱寂寞╮ 提交于 2020-01-03 19:34:12
问题 How to implement in following OpenMP code using C# Parallel.For OpenMP Code #pragma omp parallel { float[] data = new float[1000]; #pragma omp for for(int i = 0; i < 500; i++) { for(int j = 0; j < 1000; j++) { data[j] =100; // do some computation using data } } } I also tried the following but it was not exactly what OpenMP code did. In the openMP code, it was allocating Memory per thread and performs the nested loop computation. Whereas the code below, actually allocates memory for each i,

CUDA and Open MP

由 无人久伴 提交于 2020-01-03 03:43:07
问题 I dont have a Fermi at the moment but the targetting platform is tesla/Fermi, the question I want to ask is if Fermi support Open MP like this: #pragma omp parallel for num_threads(N) for (int i=0; i<1000; ++i) { int threadID=omp_get_thread_num(); cudafunctions<<<blocks, threads, 1024, streams[threadID]>>>(input+i*colsizeofinput); }//where there are N streams created. 回答1: Yes, something like that is possible. OpenMP doesn't provide any specific benefit when trying to launch multiple kernels

Multi Threading Performance in Multiplication of 2 Arrays / Images - Intel IPP

由 不打扰是莪最后的温柔 提交于 2020-01-02 06:43:51
问题 I'm using Intel IPP for multiplication of 2 Images (Arrays). I'm using Intel IPP 8.2 which comes with Intel Composer 2015 Update 6. I created a simple function to multiply too large images (The whole project is attached, see below). I wanted to see the gains using Intel IPP Multi Threaded Library. Here is the simple project (I also attached the complete project form Visual Studio): #include "ippi.h" #include "ippcore.h" #include "ipps.h" #include "ippcv.h" #include "ippcc.h" #include "ippvm.h

Openmp basic Parallelization

由 我与影子孤独终老i 提交于 2020-01-02 05:59:15
问题 I've gotten stuck writing some parallel c code using OpenMP for a concurrency course. Heres a snippet #include <stdio.h> #include <time.h> #include <math.h> #define FALSE 0 #define TRUE 1 int count_primes_0(int); int count_primes_1(int); int count_primes_2(int); int main(int argc, char *argv[]){ int n; if (argc != 2){ printf("Incorrect Invocation, use: \nq1 N"); return 0; } else { n = atoi(argv[1]); } if (n < 0){ printf("N cannot be negative"); return 0; } printf("N = %d\n", n); //omp_set_num
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