[petsc-users] Problem with Optimised version .vs. Debug version

[Barry Smith]

On Dec 7, 2011, at 9:53 AM, Jed Brown wrote:

> On Wed, Dec 7, 2011 at 06:31, Bogdan Dita <bogdan at lmn.pub.ro> wrote:
> A few weeks ago i posted a question regarding a problem with the
> optimised version of PETSc, what i mean is that I obtained a higher
> solving time with the optimised version then with the debug
> version(~10-15% higher).
> 
> What do you get from 'mpicc -show'?
> 
> MPICH2 has a tendency to put optimization flags into the wrappers. It's possible that the "optimized" build of PETSc is effectively using -O2 (from MPICH2) and -g3 (from PETSc with-debugging=1), which might be faster than -O2 (from MPICH2) -O (from PETSc with-debugging=0, taking precedence) that you get when you. You can use PETSc's --COPTFLAGS to set your own optimization flags for PETSc.
> 
> Let us know if this works.

  If this doesn't work produce the results from running the same code using the -log_summary option with and without debug. Then send the two outputs to petsc-maint at mcs.anl.gov this will tell us what parts of the code (all?) are slower and faster in the different versions.

   Barry