openmp

问题 The OpenMP standard specifies an initial value for a reduction variable. So do I have to initialize the variable and how would I do that in the following case: int sum; //... for(int it=0;i<maxIt;i++){ #pragma omp parallel { #pragma omp for nowait for(int i=0;i<ct;i++) arrayX[i]=arrayY[i]; sum = 0; #pragma omp for reduction(+:sum) for(int i=0;i<ct;i++) sum+=arrayZ[i]; } //Use sum } Note that I use only 1 parallel region to minimize overhead and to allow the nowait in the first loop. Using

问题 I have the following problem: My C program must count the number of occurrences of a list of words in a text file. I use OpenMP for this, and the program, in theory, has the correct logic. When I put some printfs inside a For Loop the result of the program is correct and always the same. When I remove printfs the result is incorrect, and with each execution its value changes. Given this scenario I think the reason is related to the execution time. With printfs the execution time is increased,

问题 I want to shorten the runtime of an lengthy image processing algorithm, which is applied to multiple images by using parallel processing with openMP. The algorithm works fine with single or limited number (=2) of threads. But: The parallel processing with openMP requires lots of memory, leading to out-of-memory-exceptions, when running with the maximum number of possible threads. To resolve the issue, I replaced the "throwing of exceptions" with a "waiting for free memory" in case of low

问题 I am trying to compile the OPENMP fortran code on linux. I have around 230 subroutines. The code I used to compile the code is as follows: 1) At first I compiled each subroutine with the following command ifort -c -override-limits -openmp *.for Then all the subroutines have now a separate object file. 2) Then I tried to compile the object files to the executable by the following command ifort *.o -o myprogram I got the following error : WINDWAVE.F90:(.text+0x1c9d): undefined reference to `_

问题 all, I was compiling a C program with OpenMP. It's my first time to use makefile. When excuting "make", the gcc reports the error make: * No rule to make target omp.h', needed by smooth.o'. Stop. However the omp.h is in the /usr/lib/gcc/i686-linux-gnu/4.6/include/omp.h , I am wondering how to fix it. Could anyone help me? Thank you. CC=gcc CFLAGS = -fopenmp all: smooth smooth: smooth.o ompsooth.o $(CC) $(CFLAGS) -o smooth smooth.o ompsmooth.o ompsmooth.o: ompsmooth.c assert.h stdio.h stdlib.h

问题 The snippet of my serial code is shown below. Program main use omp_lib Implicit None Integer :: i, my_id Real(8) :: t0, t1, t2, t3, a = 0.0d0 !$ t0 = omp_get_wtime() Call CPU_time(t2) ! ------------------------------------------ ! Do i = 1, 100000000 a = a + Real(i) End Do ! ------------------------------------------ ! Call CPU_time(t3) !$ t1 = omp_get_wtime() ! ------------------------------------------ ! Write (*,*) "a = ", a Write (*,*) "The wall time is ", t1-t0, "s" Write (*,*) "The CPU

问题 I’m trying to include openmp to my Xcode C++ project. I have changed my compiler in Xcode to LLVM GCC 4.2, added ”-fopenmp” as a CFlag and enabled OpenMP support in xcode as well. But it still says ”‘omp.h’ file not found” and i am unable to build the project. Does anyone know what could be wrong and how to fix this? 回答1: I have had the same problem. Try going to the project navigator using the panel at the left side. Select your project (the one with the blue icon), and a different main

问题 I have a matrix spread among four NUMA-node local memories. Now I want to open 4 threads, each one on a CPU corresponding to a different NUMA-node, so that each thread can access its part of the matrix as fast as possible. OpenMP has the "proc_bind(spread)" option, but it puts the threads on the same NUMA-node, but on far apart CPUs. How can I force the threads to bind to different NUMA nodes? Or, if that is not possible: When I use all cores on all nodes (256 threads total), I know how to

问题 If I'm running C++ code on a cluster, is it possible to use the value of OMP_NUM_THREADS in my program? For example, suppose I have two .cpp files main.cpp and func.cpp, where func.cpp is written in parallel using OpenMP. I want to be able to define the number of threads once (in the script below) and not have to define it again in func.cpp. #!/bin/bash #PBS -S /bin/bash #PBS -l walltime=00:10:00 #PBS -l select=1:ncpus=4:mem=2gb #PBS -q QName #PBS -N Name #PBS -o Results/output.txt #PBS -e

问题 If I'm running C++ code on a cluster, is it possible to use the value of OMP_NUM_THREADS in my program? For example, suppose I have two .cpp files main.cpp and func.cpp, where func.cpp is written in parallel using OpenMP. I want to be able to define the number of threads once (in the script below) and not have to define it again in func.cpp. #!/bin/bash #PBS -S /bin/bash #PBS -l walltime=00:10:00 #PBS -l select=1:ncpus=4:mem=2gb #PBS -q QName #PBS -N Name #PBS -o Results/output.txt #PBS -e