Fortran OpenMP程序没有显示CPU_TIME()的加速 [英] Fortran OpenMP program shows no speedup of CPU_TIME()
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问题描述
我的代码:
PROGRAM MAIN
使用omp_lib
隐式无
REAL * 8 Times1,Times2
INTEGER I,J
real,allocatable,dimension(:) :: a
分配(a(1000))
DO J = 1,1000
a(j)= j
ENDDO
! ***************无并行代码******************************** ****
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(*,*)'----------------------------------------- ----------'
! ***************并行代码********************************* ***
调用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
和结果:
CPU无并行启动:1.560010000000000E-002
CPU CPU无并行完成:4.86723120000000
无并行次数:4.85163110000000
$ p code> CPU并行启动:4.86723120000000
CPU PARALLEL完成:9.89046340000000
并行次数:5.0232322000 0000
为什么用CPU_TIME()测量的时间随OpenMP增加?
解决方案 cpu_time()占用CPU的时间,而不是挂墙时间。在并行应用程序中,这些不一样。详情请参阅此处 。
使用 system_clock()
解决了这个问题:
PROGRAM MAIN
use omp_lib
隐式无
REAL * 8 Times1,Times2
INTEGER I,J,iTimes1,iTimes2,rate
real,allocatable,dimension(:) :: a
分配(a(1000))
CALL system_clock(count_rate = rate)
DO J = 1,1000
a(j)= j
ENDDO
! ***************无并行代码******************************** ****
call CPU_TIME(Times1)
call SYSTEM_CLOCK(iTimes1)
write(*,*)'CPU NO PARALLEL STARTED:',Times1
DO I = 1, 1000
DO $ = 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
(*,*)'NO PARALLEL TIMES:',Times2-Times1,real(iTimes2-iTimes1)/ real(rate)
write(*,*)'----------- ----------------------------------------'
! ***************并行代码********************************* ***
调用CPU_TIME(Times1)
调用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
调用CPU_TIME(Times2)
调用SYSTEM_CLOCK(iTimes2)
write(*,*)'CPU PARALLEL finished:',Times2
write(*,* )'PARALLEL TIMES:',Times2-Times1,real(iTimes2-iTimes1)/ real(费率)
解除分配(a)
STOP
END
然后,您可以看到并行程序确实更快。
CPU无并行启动:4.0000000000000001E-003
CPU CPU无并行完成:1.4600000000000000
无并行TIMES:1.4560000000000000 1.45400000
------------------------------------------ ---------
CPU并行启动:1.4600000000000000
并行处理完毕:5.1040000000000001
并行时间:3.6440000000000001 0.920000017
The use of parallelism should lead to minimizing the time of a program but this did not happened to me. When I programmed my code in parallel using OpenMP, the run time is augmented, i.e. PARALLEL TIME > SERIAL TIME.
My code:
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
and the result :
CPU NO PARALLEL STARTED: 1.560010000000000E-002
CPU CPU NO PARALLEL finished: 4.86723120000000
NO PARALLEL TIMES: 4.85163110000000
CPU PARALLEL STARTED: 4.86723120000000
CPU PARALLEL finished: 9.89046340000000
PARALLEL TIMES: 5.02323220000000
Why is my time measured by CPU_TIME() increased with OpenMP?
解决方案
cpu_time()
takes the time on the CPU, not the walltime. In parallel applications these are not the same. See here for details.
Using system_clock()
solves this problem:
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
Then, you can see that the parallel program is indeed faster.
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
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