[cam-users] CGD Forums

Thu Dec 9 09:00:00 MST 2004

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<<  perturbation growth test, http://bb.cgd.ucar.edu//viewtopic.php?t=69 >>

PostereatonPostedWed Dec 08, 2004 4:34 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=225#225
Message: In my experience a jump of the magnitude you report in the perturbation growth test has always been associated with a real problem.  I think your 1 year run validates that.
<br />
<br />There are a couple of things I'd try.  One is to redo the perturbation growth test with debug flags on.  If the test is successful it indicates a problem with the compiler optimizations.  You can then experiment with reducing the optimization until you hit the level where the test passes.
<br />
<br />Another test to try is to make sure that you are getting identical results independent of the number of mpi tasks being used.  If this test fails it would indicate that there are problems with the mpi installation.

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Postercathryn.meyer at yale.eduPostedWed Dec 08, 2004 7:42 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=226#226
Message: Thanks for the suggestions.  I know it is not a problem with the MPI installation, since CAM gives the same bad climate results whether it is run with MPI or not.
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<br />I re-did the perturbation growth test with debug flags on, and got a much better difference plot.  The difference is only about a half-order of magnitude apart from the perturbation, and towards the end of the second day it jumps up to between 10^-6 and 10^-7.  Definitely much better than 10^-2, as I saw before.  So this means there is a problem with the compiler optimizations?  I am not sure what these are, or how to reduce the optimization.  What do I need to do?  Tweak the optimizations somehow and run the pergro test again without debug flags on until the test passes?
<br />
<br />Thanks,
<br />Cathy

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PostereatonPostedWed Dec 08, 2004 10:00 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=230#230
Message: The Fortran optimization is controled by the -fopt option to configure.  You'll need to look at the documentation for the particular compiler you're using to see how to change the optimization level.  The default optimization used by CAM can be found in the Makefile template ($camroot/models/atm/cam/bld/Makefile) in the  macro FORTRAN_OPTIMIZATION in the appropriate compiler specific section.  For example, in CAM-3.0 the default optimization for pgf90 is -fast.  To reduce this optimization to -O2 you would issue the command "configure -fopt -O2"
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<br />Yes, I would tweak the optimization flags and rerun the pergro test until it passes.  Then it's still necessary to run a full climate simulation for the final validation.

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PosterpjrPostedThu Dec 09, 2004 5:13 am MST, http://bb.cgd.ucar.edu//viewtopic.php?p=231#231
Message: to elaborate on Brian's response. 
<br />
<br />You dont say which compiler you are using, or which version of CAM3.
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<br />I am pretty sure there are known problems with optimization flags and certain versions of the Portland Group Compiler. The default settings of the first version of CAM3 broke versions of the compiler that came out after CAMs first release. In the "bugfix" release we changed the compiler flags to avoid that problem. The short version of this story is the the "-fast" flag (which is shorthad for a bunch of other flags") was redefined at one point. If you are using the original CAM release you should at least  check out the build procedure in the bugfix release and incorporate the new compiler flag settings.
<br />
<br />Phil

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Postercathryn.meyer at yale.eduPostedThu Dec 09, 2004 1:54 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=232#232
Message: We are using the bug fix version of CAM3.0 and PGI compilers version 5.2-1.
<br />
<br />In the cam1/models/atm/cam/bld/Makefile, in the linux section, there are the lines:
<br />
<br />  ifeq ($(DEBUG),TRUE)
<br />    # 4/10/04 - bounds checking temporarily disabled
<br />    #FFLAGS      += -g -Ktrap=fp -Mbounds
<br />    FFLAGS      += -g -Ktrap=fp -Mrecursive
<br />    SPEC_FFLAGS := $(FFLAGS)
<br />  else
<br />    SPEC_FFLAGS := $(FFLAGS)
<br />    # Check for override of default Fortran compiler optimizations
<br />    ifeq ($(F_OPTIMIZATION_OVERRIDE),$(null))
<br />      FORTRAN_OPTIMIZATION := -O2
<br />    endif
<br />    FFLAGS += $(FORTRAN_OPTIMIZATION)
<br />  endif
<br />
<br />So it seems the default FORTRAN_OPTIMIZATION is already -O2, if I'm looking in the right place.  How would I reduce this further?  Could I use the DEBUG FFLAGS?
<br />
<br />Cathy

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