Fortran OpenMP程序未显示CPU_时间的加速()
并行性的使用应该能够最大限度地减少程序的时间,但这并没有发生在我身上。当我使用OpenMP并行编程代码时,运行时间会增加,即并行时间>串行时间 我的代码:Fortran OpenMP程序未显示CPU_时间的加速(),fortran,Fortran,并行性的使用应该能够最大限度地减少程序的时间,但这并没有发生在我身上。当我使用OpenMP并行编程代码时,运行时间会增加,即并行时间>串行时间 我的代码: PROGRAM MAIN use omp_lib implicit none REAL*8 Times1,Times2 INTEGER I,J real, allocatable, dimension(:) :: a allocate(a(1000)) DO J = 1, 100
PROGRAM MAIN
use omp_lib
implicit none
REAL*8 Times1,Times2
INTEGER I,J
real, allocatable, dimension(:) :: a
allocate(a(1000))
DO J = 1, 1000
a(j)=j
ENDDO
! ***************NO PARALLEL CODE ************************************
call CPU_TIME(Times1)
write(*,*) 'CPU NO PARALLEL STARTED:',Times1
DO I = 1, 1000
DO J = 1, 500000
a(I)=a(I)+0.0001
end do
a(I)=a(I)+a(I)+a(I)
ENDDO
call CPU_TIME(Times2)
write(*,*) 'CPU CPU NO PARALLEL finished:',Times2
write(*,*) 'NO PARALLEL TIMES:',Times2-Times1
write(*,*) '---------------------------------------------------'
! ***************PARALLEL CODE ************************************
call CPU_TIME(Times1)
write(*,*) 'CPU PARALLEL STARTED:',Times1
!$OMP PARALLEL DEFAULT(shared), private(I,J)
!$OMP DO
DO I = 1, 1000
DO J = 1, 500000
a(I)=a(I)+0.0001
end do
a(I)=a(I)+a(I)+a(I)
ENDDO
!$OMP END DO
!$OMP END PARALLEL
call CPU_TIME(Times2)
write(*,*) 'CPU PARALLEL finished:',Times2
write(*,*) 'PARALLEL TIMES:',Times2-Times1
deallocate(a)
STOP
END
结果是:
CPU NO PARALLEL STARTED: 1.560010000000000E-002
CPU CPU NO PARALLEL finished: 4.86723120000000
NO PARALLEL TIMES: 4.85163110000000
为什么我的时间是用OpenMP增加的CPU_time()来衡量的?
CPU_time()
在CPU上花费时间,而不是在墙上花费时间。在并行应用程序中,这些是不同的。有关详细信息,请参阅
使用可解决此问题:
PROGRAM MAIN
use omp_lib
implicit none
REAL*8 Times1,Times2
INTEGER I,J, iTimes1,iTimes2, rate
real, allocatable, dimension(:) :: a
allocate(a(1000))
CALL system_clock(count_rate=rate)
DO J = 1, 1000
a(j)=j
ENDDO
! ***************NO PARALLEL CODE ************************************
call CPU_TIME(Times1)
call SYSTEM_CLOCK(iTimes1)
write(*,*) 'CPU NO PARALLEL STARTED:',Times1
DO I = 1, 1000
DO J = 1, 500000
a(I)=a(I)+0.0001
end do
a(I)=a(I)+a(I)+a(I)
ENDDO
call CPU_TIME(Times2)
call SYSTEM_CLOCK(iTimes2)
write(*,*) 'CPU CPU NO PARALLEL finished:',Times2
write(*,*) 'NO PARALLEL TIMES:',Times2-Times1, real(iTimes2-iTimes1)/real(rate)
write(*,*) '---------------------------------------------------'
! ***************PARALLEL CODE ************************************
call CPU_TIME(Times1)
call SYSTEM_CLOCK(iTimes1)
write(*,*) 'CPU PARALLEL STARTED:',Times1
!$OMP PARALLEL DEFAULT(shared), private(I,J)
!$OMP DO
DO I = 1, 1000
DO J = 1, 500000
a(I)=a(I)+0.0001
end do
a(I)=a(I)+a(I)+a(I)
ENDDO
!$OMP END DO
!$OMP END PARALLEL
call CPU_TIME(Times2)
call SYSTEM_CLOCK(iTimes2)
write(*,*) 'CPU PARALLEL finished:',Times2
write(*,*) 'PARALLEL TIMES:',Times2-Times1, real(iTimes2-iTimes1)/real(rate)
deallocate(a)
STOP
END
然后,您可以看到并行程序确实更快
CPU NO PARALLEL STARTED: 4.0000000000000001E-003
CPU CPU NO PARALLEL finished: 1.4600000000000000
NO PARALLEL TIMES: 1.4560000000000000 1.45400000
---------------------------------------------------
CPU PARALLEL STARTED: 1.4600000000000000
CPU PARALLEL finished: 5.1040000000000001
PARALLEL TIMES: 3.6440000000000001 0.920000017
CPU NO PARALLEL STARTED: 4.0000000000000001E-003
CPU CPU NO PARALLEL finished: 1.4600000000000000
NO PARALLEL TIMES: 1.4560000000000000 1.45400000
---------------------------------------------------
CPU PARALLEL STARTED: 1.4600000000000000
CPU PARALLEL finished: 5.1040000000000001
PARALLEL TIMES: 3.6440000000000001 0.920000017