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

[Mark Adams]

On Thu, Jan 21, 2021 at 1:44 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, Jan 21, 2021 at 11:16 AM Mark Adams <mfadams at lbl.gov> wrote:
>
>> 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)
>>
>
> Instead of using SELF, how about Comm_dup() for each thread?
>

OK, raw MPI_Comm_dup. I tried PetscCommDup. Let me this.
Thanks,


>
>   Matt
>
>
>> On Thu, Jan 21, 2021 at 10:46 AM Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Thu, Jan 21, 2021 at 10:34 AM Mark Adams <mfadams at lbl.gov> 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 <mfadams at lbl.gov> wrote:
>>>>
>>>>>
>>>>>
>>>>> 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.
>>>>>
>>>>>
>>>
>>> --
>>> 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/>
>>>
>>
>
> --
> 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/>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20210121/98596799/attachment-0001.html>