[petsc-dev] GAMG key not found in table

Tue Jun 26 07:45:15 CDT 2018

On Tue, Jun 26, 2018 at 2:54 AM Pierre Jolivet <pierre.jolivet at enseeiht.fr>
wrote:

> Hello,
> The fix suggested by Mark resolves the error:
> #define GAMG_HASH(key) (PetscInt)((((PetscInt64)7)*(PetscInt64)key)%
> (PetscInt64)a_tab->size)
>
> I’m guessing this is similar to the fix suggested by Barry:
> #define GAMG_HASH(key) ((((PetscInt64)7)*key)%a_tab->size)
>
> FWIW, my problem has around 1.2B d.o.f., so if the key is something like a
> column or row index, that could explain the error when doing 7*key
>

Thanks, and yep the integer rolls over. (unsigned PetscInt) should work
also.

>
> Thanks,
> Pierre
>
> On 24 Jun 2018, at 11:28 PM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:
>
>
>  Pierre,
>
>    Can you confirm if my suggested fix resolved the error message or not?
> If so, we'll add it to the maint branch.
>
>   Thanks
>
>    Barry
>
>
>
> https://stackoverflow.com/questions/11720656/modulo-operation-with-negative-numbers
>
>
>
> On Jun 24, 2018, at 4:19 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
>
>
> On Sun, Jun 24, 2018 at 2:09 PM Smith, Barry F. <bsmith at mcs.anl.gov>
> wrote:
>
>
> On Jun 24, 2018, at 11:15 AM, Mark Adams <mfadams at lbl.gov> wrote:
>
> First, -pc_gamg_threshold 0.8  is crazy. 0.08 is very high. probably best
> to start with 0.
>
> This threshold will delete all of your edges in the coarsening graph,
> probably, and GAMG will switch to a one level solve (silently although
> -info will tell you).
>
> And yes, this looks like a 64 bit indices problem, we have:
>
> #define GAMG_HASH(key) ((((PetscInt)7)*key)%a_tab->size)
>
> We should probably cast everything to (long long) or (unsigned PetscInt) I
> guess ... I'm not sure how this should be done exactly.  Any ideas from the
> peanut gallery?
>
>
> Mark,
>
>     It should only be changed if we know the exact mechanism that causes
> the failure. It is not obvious to me that just changing
> ((((PetscInt)7)*key)%a_tab->size) to ((((PetscInt64)7)*key)%a_tab->size)
> should matter.
>
> If 7*key > 2B then you can get a negative number and %a_tab->size will
> still be a negative number, which triggers:
>
> ksp/pc/impls/gamg/agg.c:          if (flid < 0)
> SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Cannot find gid1 in table”);
>
> which is the second error that Pierre gets. I don't fully understand the
> first error but a messed up hash table is certainly a possibility.
>
> And maybe we should cast the hell out of it to be safe:
>
> #define GAMG_HASH(key)
> (PetscInt)((((PetscInt64)7)*(PetscInt64)key)%(PetscInt64)a_tab->size)
>
> I am a bit puzzled that this works. I would think this would be more of a
> problem but maybe everyone just uses 64 bit ints. I have dealt with this
> many times and I am puzzled that I left it in a state that looks so wrong
> to me now. Perhaps Pierre's complicated thing is causing this somehow.
>
>
>
>   Barry
>
>
>
>
> On Sun, Jun 24, 2018 at 2:34 AM Pierre Jolivet <pierre.jolivet at enseeiht.fr>
> wrote:
> Hello,
> Any ideas on how to debug this?
> [406]PETSC ERROR: key 328214936 not found in table
> [406]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> [406]PETSC ERROR: Petsc Development GIT revision: v3.9.2-603-gceafe64  GIT
> Date: 2018-06-10 12:46:16 -0500
> [406]PETSC ERROR:
> /ccc/work/cont003/rndm/rndm/FreeFem-sources/src/mpi/FreeFem++-mpi on a
> arch-linux2-c-debug-bullxmpi named curie2698 by jolivetp Sun Jun 24
> 07:06:07 2018
> [406]PETSC ERROR: Configure options --with-scalar-type=real
> --with-hypre-dir=arch-linux2-c-opt-bullxmpi
> --with-metis-dir=arch-linux2-c-opt-bullxmpi
> --with-mumps-dir=arch-linux2-c-opt-bullxmpi --with-mkl_cpardiso=1
> --with-mkl_pardiso=1 --with-parmetis-dir=arch-linux2-c-opt-bullxmpi
> --with-ptscotch-dir=arch-linux2-c-opt-bullxmpi
> --with-sowing-dir=arch-linux2-c-opt-bullxmpi
> --with-blacs-include=/ccc/products/mkl-18.0.1.163/default/
> 18.0.1.163/mkl/include
> --with-blacs-lib=/ccc/products/mkl-18.0.1.163/default/
> 18.0.1.163/mkl/lib/intel64/libmkl_blacs_openmpi_lp64.so
> --with-blaslapack-dir=/ccc/products/mkl-18.0.1.163/default/
> 18.0.1.163/mkl/lib/intel64 --with-x=0 --with-debugging=1
> --with-errorchecking=1
> --with-mkl_pardiso-dir=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl
> --with-mkl_cpardiso-dir=/ccc/products/mkl-18.0.1.163/default/
> 18.0.1.163/mkl
> --with-scalapack-include=/ccc/products/mkl-18.0.1.163/default/
> 18.0.1.163/mkl/include
> --with-scalapack-lib="[/ccc/products/mkl-18.0.1.163/default/
> 18.0.1.163/mkl/lib/intel64/libmkl_scalapack_lp64.so,/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/lib/intel64/libmkl_blacs_openmpi_lp64.so]"
> --with-fortran-bindings=0 PETSC_ARCH=arch-linux2-c-debug-bullxmpi
> [406]PETSC ERROR: #1 PCGAMGHashTableFind() line 106 in
> /ccc/work/cont003/rndm/rndm/petsc/include/petsc/private/pcgamgimpl.h
> [406]PETSC ERROR: #2 smoothAggs() line 526 in
> /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/impls/gamg/agg.c
> [406]PETSC ERROR: #3 PCGAMGCoarsen_AGG() line 970 in
> /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/impls/gamg/agg.c
> [406]PETSC ERROR: #4 PCSetUp_GAMG() line 518 in
> /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/impls/gamg/gamg.c
> [406]PETSC ERROR: #5 PCSetUp() line 932 in
> /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/interface/precon.c
> [406]PETSC ERROR: #6 KSPSetUp() line 381 in
> /ccc/work/cont003/rndm/rndm/petsc/src/ksp/ksp/interface/itfunc.c
>
> For smaller problems, this works fine. Should I compile using 64 bit
> indices?
> I’m using -pc_type gamg -pc_gamg_threshold 0.8 -pc_gamg_agg_nsmooths 1
> -pc_gamg_sym_graph true -pc_gamg_square_graph 10
>
> Thanks,
> Pierre
>
>
>
>
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