openmp

How to break out of a nested parallel (OpenMP) Fortran loop idiomatically?

由 冷暖自知 提交于 2019-12-10 04:01:46
问题 Here's sequential code: do i = 1, n do j = i+1, n if ("some_condition(i,j)") then result = "here's result" return end if end do end do Is there a cleaner way to execute iterations of the outer loop concurrently other than: !$OMP PARALLEL private(i,j) !$OMP DO do i = 1, n !$OMP FLUSH(found) if (found) goto 10 do j = i+1, n if ("some_condition(i,j)") then !$OMP CRITICAL !$OMP FLUSH(found) if (.not.found) then found = .true. result = "here's result" end if !$OMP FLUSH(found) !$OMP END CRITICAL

openMP conditional pragma “if else”

由 可紊 提交于 2019-12-10 02:20:10
问题 I have a for loop that can be executed using schedule(static) or schedule(dynamic, 10) depending on a condition. Currently, My code is not DRY (Don't repeat yourself) enough and to accommodate the previous functionality it has the following repetition: boolean isDynamic; //can be true or false if(isDynamic){ #pragma omp parallel for num_threads(thread_count) default(shared) private(...) schedule(dynamic, 10) for(...){ //for code inside } }else{ #pragma omp parallel for num_threads(thread

C++ Armadillo and OpenMp: Parallelization of summation of outer products - define reduction for Armadillo matrix

由 ￣綄美尐妖づ 提交于 2019-12-09 23:37:23
问题 I am trying to parallelize a for loop using OpenMP which sums over Armadillo matrices. I have the following code: #include <armadillo> #include <omp.h> int main() { arma::mat A = arma::randu<arma::mat>(1000,700); arma::mat X = arma::zeros(700,700); arma::rowvec point = A.row(0); # pragma omp parallel for shared(A) reduction(+:X) for(unsigned int i = 0; i < A.n_rows; i++){ arma::rowvec diff = point - A.row(i); X += diff.t() * diff; // Adding the matrices to X here } } I am getting this error:

Atomic operators, SSE/AVX, and OpenMP

由 本小妞迷上赌 提交于 2019-12-09 22:57:01
问题 I'm wondering if SSE/AVX operations such as addition and multiplication can be an atomic operation? The reason I ask this is that in OpenMP the atomic construct only works on a limited set of operators. It does not work on for example SSE/AVX additions. Let's assume I had a datatype float4 that corresponds to a SSE register and that the addition operator is defined for float4 to do an SSE addition. In OpenMP I could do a reduction over an array with the following code: float4 sum4 = 0.0f; /

Intermediate Code as a result of OpenMP pragmas

由 戏子无情 提交于 2019-12-09 19:22:25
问题 Is there a way to get my hands on the intermediate source code produced by the OpenMP pragmas? I would like to see how each kind of pragmas is translated. Cheers. 回答1: OpenMp pragmas is part of a C / C++ compiler's implementation. Therefore before using it, you need to ensure that your compiler will support the pragmas ! If they are not supported, then they are ignored, so you may get no errors at compilation, but multi-thread wont work. In any case, as mentioned above, since they are part of

Implicit barrier at the end of #pragma for

由 二次信任 提交于 2019-12-09 18:15:07
问题 Friends, I am trying to learn the openMP paradigm. I used the following code to understand the #omp for pragma. int main(void){ int tid; int i; omp_set_num_threads(5); #pragma omp parallel \ private(tid) { tid=omp_get_thread_num(); printf("tid=%d started ...\n", tid); fflush(stdout); #pragma omp for for(i=1; i<=20; i++){ printf("t%d - i%d \n", omp_get_thread_num(), i); fflush(stdout); } printf("tid=%d work done ...\n", tid); } return 0; } In the above code, there is an implicit barrier at the

OpenMP drastic slowdown for specific thread number

由 倾然丶 夕夏残阳落幕 提交于 2019-12-09 11:53:05
问题 I ran an OpenMP program to perform the Jacobi method, and it was working very well, 2 threads performed slightly over 2x 1 thread, and 4 threads 2x faster than 1 thread. I felt everything was working perfectly... until I reached exactly 20, 22, and 24 threads. I kept breaking it down until I had this simple program #include <stdio.h> #include <omp.h> int main(int argc, char *argv[]) { int i, n, maxiter, threads, nsquared, execs = 0; double begin, end; if (argc != 4) { printf("4 args\n");

binding threads to certain MPI processes

由 为君一笑 提交于 2019-12-09 07:37:26
I have the following setup, a hybrid MPI/OpenMP code which runs M MPI processes with N threads each. In total there are MxN threads available. What I would like to do, if possible, is to assign threads only to some MPI processes not to all of them, my code would be more efficient since some of the threads are just doing repetitive work. Thanks. Hristo Iliev Your question is a generalised version of this one . There are at least three possible solutions. With most MPI implementations it is possible to start multiple executables with their own environments (contexts) as part of the same MPI job.

Ignore OpenMP on machine that does not have it

由 谁都会走 提交于 2019-12-09 04:32:32
问题 I have a C++ program using OpenMP, which will run on several machines that may have or not have OpenMP installed. How could I make my program know if a machine has no OpenMP and ignore those #include <omp.h> , OpenMP directives (like #pragma omp parallel ... ) and/or library functions (like tid = omp_get_thread_num(); ) ? 回答1: OpenMP is a compiler runtime thing and not a platform thing. ie. If you compile your app using Visual Studio 2005 or higher, then you always have OpenMP available as

openMP:why am I not getting different thread ids when i uses “ #pragma omp parallel num_threads(4)”

由 六月ゝ 毕业季﹏ 提交于 2019-12-09 02:44:41
问题 Why am I not getting different thread ids when I uses " #pragma omp parallel num_threads(4)". All the thread ids are 0 in this case. But when I comment the line and use default number of threads, I got different thread ids. Note:- variable I used variable tid to get thread id. #include <omp.h> #include <stdio.h> #include <stdlib.h> int main (int argc, char *argv[]) { int nthreads, tid; int x = 0; #pragma omp parallel num_threads(4) #pragma omp parallel private(nthreads, tid) { /* Obtain
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