Timing

Testando vetorização:

• Maior problema alocável: 154Mb * 3*4 = 1.8Gb

! http://goparallel.sourceforge.net/optimizing-loops-vectorization/
program Vectorization
use portlib
real(4),dimension(:),allocatable  ::  x,y,z
integer                           ::  len=150*1024*1024 ! 154 Mb
real(4)                           ::  timing

allocate( x(len) ,stat=ierr)
allocate( y(len) ,stat=ierr)
allocate( z(len) ,stat=ierr)

do j=1,10
timing = secnds(0.0)
do i=1,len
  z(i)=sqrt(x(i))+sqrt(y(i))
end do
timing = secnds(timing)*1000
print *,' Timing =',timing,'/1000 s'
end do
end program

• Resultados: Usando real(4) ou real(8) leva aprox. o mesmo tempo.

Memory                            1.75  Gb

Debug (no optimization) (32bits)  2.13  s
Debug (no optimization) (64bits)  2.00  s
Release                 (32bits)  0.143 s
Release                 (64bits)  0.140 s   <=========

Release (64bits)
  /Qvec-   (sem vetorizacao)      0.909 s  (NOT the default)
  Threshold for vectorization 0   0.140 s
  Threshold for parallelization 0 0.140 s
  Parallelization yes             0.171 s   /Qparallel (or any combination above) usa 8 processors
  Inline directive                0.145 s   /Ob1                                  use 4 processors

• real(16): As coisas ficam lll...e...n.t...as.. . .. . . (vectorization doesn't help)

Memory                            7.3 Gb  (permon) Windows performance monitor
Release (64bits)                  7.00  s 
  /Qvec-   (sem vetorizacao)      7.02  s  (NOT the default)