[petsc-users] Amortizing calls to PetscOptionsFindPair_Private()

[Bhalla, Amneet Pal S]

Hi Barry,

In our code at each timestep we build MG level smoothers using PETSc KSP solvers. We are using a PETSc function KSPSetFromOptions()
after we set some default values to the KSP. However, the profiler is showing that PetscOptionsFindPair_Private() is taking about 14% of total runtime.
We ran the code for 100 timesteps, and preconditioner is built everytime step. I am posting a sequence of calls to KSPSolve_Richardson that shows
getting PETScOptions adds up to a lot of cost

"KSPSolve_Richardson" 	       8.80e+05 12.7% 	
   "PCApplyBAorAB" 	               5.25e+05  7.6% 	
     "PCApply" 	                               4.85e+05  7.0% 	
       "PCApply_ASM" 	               4.85e+05  7.0% 	
         "KSPSolve" 	                       4.53e+05  6.6% 	
           "KSPSolve_PREONLY"                      2.06e+05  3.0% 	
           "PetscObjectViewFromOptions" 	       3.19e+04  0.5% 	
           "PetscObjectViewFromOptions" 	       2.39e+04  0.3% 	
           "PetscOptionsGetBool" 	               2.39e+04  0.3% 	
           "PetscOptionsHasName" 	               2.39e+04  0.3% 	
          "PetscOptionsGetBool" 	               2.39e+04  0.3% 	
          "PetscOptionsHasName" 	               1.60e+04  0.2% 	
          "PetscOptionsGetBool" 	               1.60e+04  0.2% 	
          "PetscObjectViewFromOptions" 	       1.60e+04  0.2% 	
          "KSPReasonViewFromOptions" 	       1.60e+04  0.2% 	
          "PetscOptionsGetBool" 	               1.56e+04  0.2% 	
          "PetscObjectViewFromOptions" 	        7.98e+03  0.1% 	
          "KSPSetUpOnBlocks" 	                        7.98e+03  0.1% 	
          "PetscOptionsGetBool" 	                7.98e+03  0.1% 	
          "VecSet" 	                                        7.97e+03  0.1% 	
          "PetscObjectViewFromOptions" 	        7.92e+03  0.1%

Do you have some suggestions as to doing it in a fast way -- maybe parsing options only once in the simulation and making populating KSP 
options essentially a no-op?

Thanks,
--Amneet