Performance loss with gfortran on 64-bit Linux

[Deji Akingunola <deji_aking at yahoo dot ca>]

Hi,

I've been running a 1-D atmospheric model with gfortran and I'm observing it runs many orders slower in 64-bit than it does in 32 bit mode. The system is x86_64 Fedora rawhide (which contains the latest gfortran from the 4.1 tree). I've provided some numbers below of time it takes to complete a certain number of time-steps of the code, (including numbers with using pgf90, as a comparison). The 32-bit  results are from compiling and linking with -m32 flags, though I obtained almost same numbers when ran on 32-bit install of updated Fedora Core 5, on the same machine.

32-bit gfortran
  real    0m39.474s
  user    0m38.554s
  sys     0m0.900s

32-bit gfortran with '-fastmath'
  real    0m26.247s
  user    0m25.214s  
  sys     0m0.916s

32-bit pgf90
  real    0m23.245s
  user    0m22.341s
  sys     0m0.308s

32-bit pgf90 with '-fast'
  real    0m19.839s
  user    0m19.485s
  sys     0m0.308s


64-bit gfortran
  real    1m20.896s
  user    1m19.857s
  sys     0m0.872s

64-bit gfortran with '-fastmath'
  real    1m17.389s 
  user    1m16.353s
  sys     0m0.872s

64-bit pgf90
  real    0m16.774s
  user    0m16.297s
  sys     0m0.332s

64-bit pgf90 with '-fast'
  real    0m15.725s
  user    0m15.385s
  sys     0m0.328s.

For anyone who wants to see the code, its on ftp://czar.eas.yorku.ca/pub/one-d/