Questions tagged [openmp]

OpenMP is a cross-platform multi-threading API which allows fine-grained task parallelization and synchronization using special compiler directives.

OpenMP is a cross-platform multi-threading API which allows fine-grained task parallelization and synchronization using special compiler directives. OpenMP offers easy access to multi-threading without requiring knowledge of system-dependent details. At the same time, it is reasonably efficient compared to fine-tuned implementations with the bonus of being easiest to write multi-threads code. Forums and complete information on OpenMP is at https://openmp.org/.

OpenMP is based on multi-thread model, and offers Shared Memory parallelism and heterogeneous programming for coprocessors through compiler directives, library routines and environment variables. It is restricted to C/C++ and Fortran applications, however provides portability across different Shared Memory architectures.

It is through directives, added by the programmer to the code, that the compiler adds parallelism in the application. OpenMP can be used in single or multi-cores machines, in the first architecture the compiler directives are ignored, thus the application is executed in a sequential manner, promoting portability between the two architectures.

Latest version is 5.2 (November 2021): Official OpenMP specifications.

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How to get OpenMP to work with #pragma omp task?

I'm using OpenMP with Linux terminal. I compile my program with the flag -fopenmp. The environment I'm using does support multithreading. #pragma omp parallel num_threads(3) { #pragma omp task R11Inverted =…
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Omp sections vs Omp workshare

I read: "This construct (Omp workshare) is used to parallelize array operations by dividing the task into units of work. Each such unit of work is handled only by one of the available threads present in the parallel region." (from 'Ray, S. (2019).…
user
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OpenMP taskloop: synchronization between two consecutive taskloop constructs

How is synchronization between two taskloop constructs done? Specifically, in the following pseudo code, if there are more threads available than the number of tasks of the first loop, I believe these free threads are spinning at the implicit…
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OpenMP with BLAS

related question I tried to extend the code in the answer of the above link, to include cross checks and openmp. Program reshape_for_blas Use, Intrinsic :: iso_fortran_env, Only : wp => real64, li => int64 Implicit None Real( wp ),…
AlphaF20
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Using an openmp pragma inside #define

Possible Duplicates: C/C++ pragma in define macro Conditional “pragma omp” How can I use an OpenMP pragmas inside a macro definition? E.g. #define A() { \ ...a lot of code... \ #pragma omp for \ for(..) \ ..do_for.. …
osgx
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OpenMP slows down unrelated serial loop

I have two unrelated for loops, one is executed serial and one is executed with an OpenMP parallel for construct. The next serial code becomes slower the more OpenMP-Threads I'm using. class Foo { public: Foo(size_t size) { …
Fabian
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Configure FFTW `configure: error: don't know how to enable OpenMP`

I've been using FFTW3 for two months now. I've recently decided to try and implement some parallel aspects to it to speed up computation. However... When I try to ./configure --enable-threads --enable-openmp --prefix=/$HOME/Desktop/FFTWLibParallel …
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Simplest example of parallel run using OpenMP

Consider the following code construct, int n = 0; #pragma omp parallel for collapse(2) for (int i = 0; i < 3; i++) for(int j = 0; j < 3; j++) n++; Now the above is the simplest possible demo of a similar thing I am trying to…
user6418066
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How to continue work with master while threads execute for loop iterations?

I am asked to write an OpenMP program in C such that the main thread distributes the work to other threads, and while they are working on their tasks, the main should periodically check whether they are done, and if not, it should increment a shared…
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How to integrate my calculation C code with OpenMP

I am using a dual channels DAQ card with data stream mode. I wrote some code for analysis/calculation and put them to the main code for operation. However, the FIFO overflow warning sign always occur once its total data reach around 6000 MSamples…
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How to do a parallel bilinear interpolation

I tried this but I don't know if it is right, and to calculate the time of execution sometimes it gives me 0 in the code. I firstly created a structure to stock all the coordinates of the point to be interpolated I have a table of points to be…
user9066490
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Monte Carlo simulation runs significantly slower than sequential

I'm new to the concept of concurrent and parallel programing in general. I'm trying to calculate Pi using Monte Carlo method in C. Here is my source code: #include #include #include #include int main(void) { …
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Why would omp_set_num_threads( omp_get_num_threads() ) change anything?

I've run across something odd. I am testing an MPI + OMP parallel code on a small local machine with only a single, humble 4 core I3. One of my loops, it turns out, is very slow with more than 1 OMP thread per process in this environment (more…
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Difference between #pragma omp parallel and #pragma omp parallel for

I am new to OpenMP and I have been trying to run a program which adds two arrays using OpenMP. In the OpenMP tutorial, I have learned that we need to use #pragma omp parallel for while using OpenMP on the for loop. But I have also tried the same…
user14724017
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CHUNKSIZE in openMP static scheduling

Assume that each loop iteration of my code takes the same time. Please note that each loop iteration involves memory access from disjoint portions of a large contiguous memory. I am using VS2019 compiler. I thought it should not matter whether I…
fonishormon
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