[cam-users] CGD Forums

Fri Dec 10 09:00:00 MST 2004

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

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.
 
 In the cam1/models/atm/cam/bld/Makefile, in the linux section, there are the lines:
 
 ifeq ($(DEBUG),TRUE)
 # 4/10/04 - bounds checking temporarily disabled
 #FFLAGS += -g -Ktrap=fp -Mbounds
 FFLAGS += -g -Ktrap=fp -Mrecursive
 SPEC_FFLAGS := $(FFLAGS)
 else
 SPEC_FFLAGS := $(FFLAGS)
 # Check for override of default Fortran compiler optimizations
 ifeq ($(F_OPTIMIZATION_OVERRIDE),$(null))
 FORTRAN_OPTIMIZATION := -O2
 endif
 FFLAGS += $(FORTRAN_OPTIMIZATION)
 endif
 
 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?
 
 Cathy

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PosterjmccaaPostedThu Dec 09, 2004 6:04 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=235#235
Message: Cathy's problem is exactly what I was seeing using the pgi 5.1-6 compiler on NCAR's clusters (bangkok and calgary) both with "-fast" and with "-O2".  The only runs in which I did not see the anomolous warming at the top of the model were runs in which I took out all optimization flags.  I believe this corresponds to "-O1", but I am not sure.
<br />
<br />Using the portland group compiler, with no optimization flags, I was able to verify the climate against the control runs (using the oracle method, not the statistical test).  This was consistent with George Carr's more formal evaluation of the coupled system.  Since the temperature problem with optimization turned up was so glaring, there was no point in trying to verify that.
<br />
<br />So... at present I could not IMHO recommend using the PGI compiler to run CAM with any level of optimization.  
<br />
<br />Jim

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Postercathryn.meyer at yale.eduPostedThu Dec 09, 2004 10:59 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=237#237
Message: I did a perturbation growth test without any optimizations to PGF90 and the test seems to have passed, the difference curve is almost identical to the curve from the DEBUG option run, with the max difference getting to 10^-7 towards the end of the second day of the run.
<br />
<br />Is it okay to run CAM3.0 with no compiler optimizations (as long as the climate verifies)?  What do the optimizations do?
<br />
<br />Thanks,
<br />Cathy

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PosterpjrPostedFri Dec 10, 2004 6:20 am MST, http://bb.cgd.ucar.edu//viewtopic.php?p=238#238
Message: When you say "without any optimization" do you mean 
<br />
<br />1) deleting any reference to optimization flags (eg -Ox and -fast [where X is a number])
<br />
<br />or
<br />
<br />2) explicitly disabling the optimization  use "-O0" (minus folllowed by the letter "O" followed by the number "zero").
<br />
<br />option two is the prefered way. Option 1 is basically saying "take the default optimization (which is generally not the same as disabling optimization).
<br />
<br />The model will run significantly slow (frequently 20-100% slower) without optimization.
<br />
<br />Phil

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Postercathryn.meyer at yale.eduPostedFri Dec 10, 2004 3:11 pm MST, http://bb.cgd.ucar.edu//viewtopic.php?p=239#239
Message: I did the first option.  It seems to have worked, although I haven't run a full climate simulation yet.  I'll try the second option too and see what that gives me.
<br />
<br />Cathy

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