[在Linux中使用Matlab MEX时，OpenMP不加速

Question

我正在使用OpenMP来加速Matlab MEX文件中的Fortran代码。但是，我发现OpenMP似乎不适用于Linux，但实际上适用于Windows。我将代码附加如下：

1）Matlab Mex文件：

clc; clear all; close all;   tic

FLAG_SYS = 0; % 0 for Windows; 1 for Linux

%--------------------------------------------------------------------------
% Mex Fortran code 
%--------------------------------------------------------------------------
if FLAG_SYS == 0
    mex COMPFLAGS="-Qopenmp $COMPFLAGS"...
        LINKFLAGS="/Qopenmp $LINKFLAGS"...   
        OPTIMFLAGS="/Qopenmp $OPTIMFLAGS"...
        '-IC:\Program Files (x86)\IntelSWTools\compilers_and_libraries_2017.5.267\windows\mkl\include'...
        '-LC:\Program Files (x86)\IntelSWTools\compilers_and_libraries_2017.5.267\windows\mkl\lib\intel64'...
        -lmkl_intel_ilp64.lib -lmkl_intel_thread.lib -lmkl_core.lib libiomp5md.lib...
        Test_OpenMP_Mex.f90...
        -output Test_OpenMP_Mex  

elseif FLAG_SYS == 1        
    mex COMPFLAGS="-fopenmp $COMPFLAGS"...
        LINKFLAGS="-fopenmp $LINKFLAGS"...  
        FFLAGS='$FFLAGS -fdec-math -cpp' ...
        '-I${MKLROOT}/include'...
        '-L${MKLROOT}/lib'...
        -lmkl_avx2 -lmkl_gf_ilp64 -lmkl_core -lmkl_intel_thread -liomp5 -lpthread -lm -ldl...
        Test_OpenMP_Mex.f90...
        -output Test_OpenMP_Mex           
end

Test_OpenMP_Mex;

2）Fortran代码

#include "fintrf.h"

     !GATEWAY ROUTINE
      SUBROUTINE MEXFUNCTION(NLHS, PLHS, NRHS, PRHS)

     !DECLARATIONS
      IMPLICIT NONE

     !MEXFUNCTION ARGUMENTS:
      MWPOINTER PLHS(*), PRHS(*)
      INTEGER NLHS, NRHS

     !FUNCTION DECLARATIONS:
      MWPOINTER MXCREATEDOUBLEMATRIX

      MWPOINTER MXGETM, MXGETN
      INTEGER MXISNUMERIC 

     !POINTERS TO INPUT MXARRAYS:
      MWPOINTER MIV1, MIV2

     !POINTERS TO OUTPUT MXARRAYS:
      MWPOINTER MOV1, MOV2

     !CALL FORTRAN CODE
     CALL  TEST_OPENMP


      RETURN

      END

!-----------------------------------------------------------------------
    SUBROUTINE TEST_OPENMP

        USE OMP_LIB

        IMPLICIT NONE

        INTEGER I, J, K, STEP
        REAL*8  STARTTIME, ENDTIME,Y


        OPEN(1,FILE='1.TXT') 

        !COUNT ELAPSED TIME START
        STARTTIME = OMP_GET_WTIME() 

        DO I = 1,1000000
            DO J = 1,50000
                DO K = 1,1000
                    Y=(I+10)*J-SQRT(789.1)+SQRT(789.1)-(I+10)*J
                END DO
            END DO
        END DO     


        ENDTIME = OMP_GET_WTIME()
        WRITE(1,*) ENDTIME-STARTTIME

        !COUNT ELAPSED TIME START
        STARTTIME = OMP_GET_WTIME() 

!$OMP PARALLEL
!$OMP DO PRIVATE(I,J)
        DO I = 1,1000000
            DO J = 1,50000
                DO K = 1,1000
                    Y=(I+10)*J-SQRT(789.1)+SQRT(789.1)-(I+10)*J
                END DO
            END DO
        END DO     
!$OMP END DO  
!$OMP END PARALLEL        

        ENDTIME = OMP_GET_WTIME()
        WRITE(1,*) ENDTIME-STARTTIME 

!$OMP PARALLEL        
        ! GET THE NUMBER OF THREADS
        WRITE(1,*) OMP_GET_THREAD_NUM(), OMP_GET_NUM_THREADS() 
!$OMP END PARALLEL         
        CLOSE(1)

        RETURN

      END SUBROUTINE TEST_OPENMP

Windows上的输出是：

   1.09620520001044     
   4.50355500000296     
   0           6
   1           6
   3           6
   5           6
   2           6
   4           6

并且在Linux上的输出是：

   0.0000   
   0.0000    
   0           1

显然，OpenMP可在Windows上运行，因为计算时间从4.5s减少到1.0s。我发现有6个线程用于计算。但是，在Linux上，似乎没有执行任何计算，并且只有2个线程（Linux上的线程数为36，但仅使用了2个）。

欢迎提出任何建议！

您可以直接从此链接下载代码：https://www.dropbox.com/sh/crkuwhu22407sjs/AAAQrtzAvTmFOmAxv_jpTCBaa?dl=0

Answer 1

在Linux（和MacOS）下编译MEX文件时，COMPFLAGS变量将被忽略。它是Windows特定的环境变量。您需要将CFLAGS用于C，将CXXFLAGS用于C ++，或将FFLAGS用于Fortran，将LDFLAGS用于链接器。这些是控制编译的标准Unix环境变量。

您的编译命令将如下所示：

mex LDFLAGS='-fopenmp $LDFLAGS'...
    FFLAGS='-fopenmp -fdec-math -cpp $FFLAGS' ...
    '-I${MKLROOT}/include'...
    '-L${MKLROOT}/lib'...
    -lmkl_avx2 -lmkl_gf_ilp64 -lmkl_core -lmkl_intel_thread -liomp5 -lpthread -lm -ldl...
    Test_OpenMP_Mex.f90...
    -output Test_OpenMP_Mex

参考：

• MATLAB documentation
• GCC environment variables