[petsc-dev] Memory problem with OpenMP and Fieldsplit sub solvers

[Mark Adams]

On Wed, Jan 20, 2021 at 6:21 PM Barry Smith <bsmith at petsc.dev> wrote:

>
>
> On Jan 20, 2021, at 3:09 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
> So I put in a temporary hack to get the first Fieldsplit apply to NOT use
> OMP and it sort of works.
>
> Preonly/lu is fine. GMRES calls vector creates/dups in every solve so that
> is a big problem.
>
>
>   It should definitely not be creating vectors "in every" solve. But it
> does do lazy allocation of needed restarted vectors which may make it look
> like it is creating "every" vectors in every solve.  You can
> use -ksp_gmres_preallocate to force it to create all the restart vectors up
> front at KSPSetUp().
>

Well, I run the first solve w/o OMP and I see Vec dups in cuSparse Vecs in
the 2nd solve.


>
>   Why is creating vectors "at every solve" a problem? It is not thread
> safe I guess?
>

It dies when it looks at the options database, in a Free in the get-options
method to be exact (see stacks).

======= Backtrace: =========
/lib64/libc.so.6(cfree+0x4a0)[0x200021839be0]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(PetscFreeAlign+0x4c)[0x2000002a368c]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(PetscOptionsEnd_Private+0xf4)[0x2000002e53f0]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(+0x7c6c28)[0x2000008b6c28]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(VecCreate_SeqCUDA+0x11c)[0x20000052c510]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(VecSetType+0x670)[0x200000549664]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(VecCreateSeqCUDA+0x150)[0x20000052c0b0]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(+0x43c198)[0x20000052c198]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(VecDuplicate+0x44)[0x200000542168]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(VecDuplicateVecs_Default+0x148)[0x200000543820]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(VecDuplicateVecs+0x54)[0x2000005425f4]
/gpfs/alpine/csc314/scratch/adams/petsc/arch-summit-opt-gnu-cuda-omp/lib/libpetsc.so.3.014(KSPCreateVecs+0x4b4)[0x2000016f0aec]



>
> Richardson works except the convergence test gets confused, presumably
> because MPI reductions with PETSC_COMM_SELF is not threadsafe.
>
>
>
> One fix for the norms might be to create each subdomain solver with a
> different communicator.
>
>
>    Yes you could do that. It might actually be the correct thing to do
> also, if you have multiple threads call MPI reductions on the same
> communicator that would be a problem. Each KSP should get a new MPI_Comm.
>

OK. I will only do this.
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