[petsc-dev] GAMG key not found in table

Tue Jun 26 01:54:24 CDT 2018

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,
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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