Performance problem between ifort 12.1 and ifort 15.0 on the same code

Hi,

I compile the following small code with "-O3 -shared-intel" on  three different clusters:

• cluster1: Intel(R) Xeon(R) CPU X5675 with ifort 12.1.0
• cluster2: Intel(R) Xeon(R) CPU X5650 with ifort 12.1.0
• cluster3: Intel(R) Xeon(R) CPU E5-2650 v2 with ifort 15.0.0

      program main
c
      implicit none

      integer jma, kma, ntstepmax
      integer na
      integer nfx,nfy,nfz
      real lnx,lny,lnz
      parameter (jma = 139, kma = 16)
      parameter (ntstepmax = 100)
      parameter (nfx = 1180, nfy = 8, nfz = 14)
      parameter (lnx = 590, lny = 4, lnz = 7)
      parameter (na = 1)
c
      integer ntstep
      integer i,j,k,i2,j2,k2,l
      real  a(na,-nfx:nfx,-nfy:nfy,-nfz:nfz)
      real  xu(-nfx:nfx,-nfy+1:jma+nfy,-nfz+1:kma+nfz)
      real  yu(1:jma+2,1:kma+2)
c
      do ntstep = 1,ntstepmax
c
        write (*,*) '  ........ ntstep = ',ntstep
c
        l = 1
c
        do k = 1,kma
          do j = 1,jma
            yu(j+1,k+1) = 0.0
c
            do k2 = -nfz,nfz
              do j2 = -nfy,nfy
                do i2 = -nfx,nfx
c$$$            do i2 = -nfx,nfx
c$$$              do j2 = -nfy,nfy
c$$$                do k2 = -nfz,nfz
                  yu(j+1,k+1) = yu(j+1,k+1) +& xu(i2,j+j2,k+k2)*a(l,i2,j2,k2)
                 enddo
               enddo
            enddo
c
          enddo
        enddo
c
      enddo
c
      end

The results are quite strange:

• cluster1: 0m29s
• cluster2: 0m37s
• cluster3: 2m32s

Between cluster1 and cluster2 the difference of time is small and it could be linked to the difference of CPU frequency between both cluster.

But why is cluster3 so slow? The hardware is quite new (last year) in comparison with cluster1 and cluster2 (hardware and software from 2011).

Is it a problem with the code above? Or a problem of optimization?

any help or suggestions would be appreciated.

Best regards,

Guillaume De Nayer