Yes, the problem is that each KSP solver is running in an OMP thread (So at this point it only works for SELF and its Landau so it is all I need). It looks like MPI reductions called with a comm_self are not thread safe (eg, the could say, this is one proc, thus, just copy send --> recv, but they don't)
On Thu, Jan 21, 2021 at 10:46 AM Matthew Knepley <[email protected]> wrote: > On Thu, Jan 21, 2021 at 10:34 AM Mark Adams <[email protected]> wrote: > >> It looks like PETSc is just too clever for me. I am trying to get a >> different MPI_Comm into each block, but PETSc is thwarting me: >> > > It looks like you are using SELF. Is that what you want? Do you want a > bunch of comms with the same group, but independent somehow? I am confused. > > Matt > > >> if (jac->use_openmp) { >> ierr = KSPCreate(MPI_COMM_SELF,&ilink->ksp);CHKERRQ(ierr); >> PetscPrintf(PETSC_COMM_SELF,"In PCFieldSplitSetFields_FieldSplit with >> -------------- link: %p. Comms %p >> %p\n",ilink,PetscObjectComm((PetscObject)pc),PetscObjectComm((PetscObject)ilink->ksp)); >> } else { >> ierr = >> KSPCreate(PetscObjectComm((PetscObject)pc),&ilink->ksp);CHKERRQ(ierr); >> } >> >> produces: >> >> In PCFieldSplitSetFields_FieldSplit with -------------- link: 0x7e9cb4f0. >> Comms 0x660c6ad0 0x660c6ad0 >> In PCFieldSplitSetFields_FieldSplit with -------------- link: 0x7e88f7d0. >> Comms 0x660c6ad0 0x660c6ad0 >> >> How can I work around this? >> >> >> On Thu, Jan 21, 2021 at 7:41 AM Mark Adams <[email protected]> wrote: >> >>> >>> >>> On Wed, Jan 20, 2021 at 6:21 PM Barry Smith <[email protected]> wrote: >>> >>>> >>>> >>>> On Jan 20, 2021, at 3:09 PM, Mark Adams <[email protected]> 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. >>> >>> > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> >
