openmp

问题 Does OpenMP support an atomic minimum for C++11? If OpenMP has no portable method: Is there some way of doing it using a x86 or amd64 feature? In the OpenMP specifications I found nothing for C++ but the Fortran version seems to support it. See 2.8.5 of the v3.1 for the details. For C++ it states binop is one of +, *, -, /, &, ^, |, <<, or >>. but for Fortran it states intrinsic_procedure_name is one of MAX, MIN, IAND, IOR, or IEOR. In case you are interested in more context: I am looking for

问题 I've read on Stackoverflow that none of the STL containers are thread-safe for writing . But what does that mean in practice? Does it mean I should store writable data in plain arrays? I expect concurrent calls to std::vector::push_back(element) could lead to inconsistent data structures becaue it might entail resizing the vector. But what about a case like this, where resizing is not involved: using an array: int data[n]; // initialize values here... #pragma omp parallel for for (int i = 0;

问题 I am attempting to make a fast password generator using multithreading with OpenMP integrated into Visual Studio 2010. Let's say I have this basic string generator that randomly pulls Chars from a string. srand(time(0)); for (i = 0; i < length; ++i) { s=pwArr[rand()%(pwArr.size()-1)]; pw+=s; } return pw; Now, the basic idea is to enable multithreading with OpenMP to enable really fast random char lookup, like so: srand(time(0)); #pragma omp parallel for for (i = 0; i < length; ++i) { s=pwArr

问题 I have a problem with my code, it should print number of appearances of a certain number. I want parallelize this code with OpenMP, and I tried to use reduction for arrays but it's obviously didn't working as I wanted. The error is: "segmentation fault". Should some variables be private? or it's the problem with the way I'm trying to use the reduction? I think each thread should count some part of array, and then merge it somehow. #pragma omp parallel for reduction (+: reasult[:i]) for (i = 0

问题 I have a problem with my code, it should print number of appearances of a certain number. I want parallelize this code with OpenMP, and I tried to use reduction for arrays but it's obviously didn't working as I wanted. The error is: "segmentation fault". Should some variables be private? or it's the problem with the way I'm trying to use the reduction? I think each thread should count some part of array, and then merge it somehow. #pragma omp parallel for reduction (+: reasult[:i]) for (i = 0

问题 I learnt OpenMP using Tim Matterson's lecture notes, and he gave an example of false sharing as below. The code is simple and is used to calculate pi from numerical integral of 4.0/(1+x*x) with x ranges from 0 to 1. The code uses a vector to contain the value of 4.0/(1+x*x) for each x from 0 to 1, then sum the vector at the end: #include <omp.h> static long num_steps = 100000; double step; #define NUM_THREADS 2 void main() { int i, nthreads; double pi, sum[NUM_THREADS]; step = 1.0/(double)num

问题 When allocating a lot of memory on 4 distinct NVIDIA V100 GPUs , I observe the following behavior with regards to parallelization via OpenMP: Using the #pragma omp parallel for directive, and therefore making the cudaMalloc calls on each GPU in parallel, results in the same performance as doing it completely serial. This is tested and the same effect validated on two HPC systems: IBM Power AC922 and an AWS EC2 p3dn.24xlarge . (The numbers are obtained on the Power machine.) ./test 4000000000

问题 When allocating a lot of memory on 4 distinct NVIDIA V100 GPUs , I observe the following behavior with regards to parallelization via OpenMP: Using the #pragma omp parallel for directive, and therefore making the cudaMalloc calls on each GPU in parallel, results in the same performance as doing it completely serial. This is tested and the same effect validated on two HPC systems: IBM Power AC922 and an AWS EC2 p3dn.24xlarge . (The numbers are obtained on the Power machine.) ./test 4000000000

问题 I have a multithreaded code in C, using OpenMP and Intel MKL functions. I have the following code: omp_set_num_threads(nth); #pragma omp parallel for private(l,s) schedule(static) for(l=0;l<lines;l++) { for(s=0;s<samples;s++) { out[l*samples+s]=mkl_ddot(&bands, &hi[s*bands+l], &inc_one, &hi_[s*bands+l], &inc_one); } }//fin for l I want to use all the cores of the multicore processor (the value of nth) in this pramga. But I want that each core computes a single mkl_ddot function independently

问题 I have a multithreaded code in C, using OpenMP and Intel MKL functions. I have the following code: omp_set_num_threads(nth); #pragma omp parallel for private(l,s) schedule(static) for(l=0;l<lines;l++) { for(s=0;s<samples;s++) { out[l*samples+s]=mkl_ddot(&bands, &hi[s*bands+l], &inc_one, &hi_[s*bands+l], &inc_one); } }//fin for l I want to use all the cores of the multicore processor (the value of nth) in this pramga. But I want that each core computes a single mkl_ddot function independently