What if a MPI process has no submatrices, how does it save the flag?
> On Jan 22, 2017, at 8:58 PM, Zhang, Hong <[email protected]> wrote:
>
> The 'saved' context is in submatrices, not original matrix. I made following
> fix:
>
> if (C->submat_singleis) { /* flag is set in PCSetUp_ASM() to skip
> MPIU_Allreduce() */
> ierr =
> MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
> + C->submat_singleis = PETSC_FALSE; /* resume its default value in case C
> will be used for non-singlis */
> PetscFunctionReturn(0);
> }
> ...
> + } else { /* MAT_REUSE_MATRIX */
> subc = (Mat_SeqAIJ*)((*submat)[0]->data);
> smat = subc->submatis1;
> if (!smat) {
> /* smat is not generated by
> MatGetSubMatrix_MPIAIJ_All(...,MAT_INITIAL_MATRIX,...) */
> wantallmatrix = PETSC_TRUE;
> + } else if (smat->singleis) {
> + ierr =
> MatGetSubMatrices_MPIAIJ_SingleIS(C,ismax,isrow,iscol,scall,submat);CHKERRQ(ierr);
> + PetscFunctionReturn(0);
> } else {
>
> ...
> ie., after first call of MatGetSubMatrices_MPIAIJ_SingleIS, this flag is set
> in saved context of submatrices
> and is reset as 'false' to the original matrix C.
>
> Do you agree with this fix? Is so, I'll push it in a branch for nightly test.
>
> Hong
>
> ________________________________________
> From: Barry Smith [[email protected]]
> Sent: Friday, January 20, 2017 8:19 PM
> To: Matthew Knepley
> Cc: Zhang, Hong; PETSc
> Subject: Re: [petsc-dev] Bug introduced in MatGetSubmatrices()
>
> Ok, so the problem comes from setting the flag in in the original matrix
> that other people have access to and can be used for other purposes by
> anyone,.
>
> So it would be better to instead put the flag into the generated sub matrix
> which no one else has access to. This should be do-able and is the right way
> to do it anyways.
>
> Hong, can you try putting all the "saved" context into the generated
> submatrices instead of the original matrix? If that is not possible then the
> context saved with the original matrix should have a reference to the sub
> matrix and this context should only be reused if the sub matrix passed in
> matches the sub matrix referenced in the context (this is a less desirable
> solution).
>
> Barry
>
>> On Jan 20, 2017, at 8:06 PM, Matthew Knepley <[email protected]> wrote:
>>
>> On Fri, Jan 20, 2017 at 7:39 PM, Barry Smith <[email protected]> wrote:
>>
>>> On Jan 20, 2017, at 7:01 PM, Matthew Knepley <[email protected]> wrote:
>>>
>>> On Fri, Jan 20, 2017 at 3:08 PM, Barry Smith <[email protected]> wrote:
>>>
>>>> On Jan 20, 2017, at 3:01 PM, Zhang, Hong <[email protected]> wrote:
>>>>
>>>> We set C->submat_singleis = false as default.
>>>> User turns it on when he knows a single IS will be used for
>>>> MatGetSubMatrices(), e.g., when asm is used.
>>>> User should turn the flag off after it is being used.
>>>
>>> Right, this is why I am confused why this is messing up Mat since
>>> presumably he is not setting it?
>>>
>>> ASM is turning this flag on, and it is corrupting my UNRELATED call to
>>> MatGetSubMatrices().
>>
>> Yes, but you need to tell us exactly how. The flag is set into
>> C->submat_singleis which is associated with the C from ASM, so why is it
>> affecting your UNRELATED call to MatGetSubMatrices(). It is not a global
>> variable so shouldn't.
>>
>> It sets the flag on the primary matrix. I will go step by step
>>
>> 1) I have a linear system with matrix A
>>
>> 2) To form a preconditioner for FieldSplit, I extract some diagonal blocks
>> from A using MatGetSubMatrices()
>>
>> 3) I also use ASM on the another block of FS
>>
>> 4) The second Newton iterate, I try to call MatGetSubMatrices(), but ASM
>> has set a flag on the matrix that causes this to fail.
>>
>> Explain or send a code that reproduces the problem.
>>
>> You can easily reproduce this by installing PyLith (a widely used package)
>> and running an automatic test. However, since this
>> is so simple, I am not sure this is necessary.
>>
>> Matt
>>
>> Barry
>>
>>>
>>> Matt
>>>
>>>>
>>>> This flag is for optimization -- avoid MPI_Allreduce, which is expensive
>>>> for np>10k.
>>>> MatGetSubMatrices() works without this flag turns on.
>>>> I just merged the improved MatGetSubMatrices_MPIAIJ() which only calls
>>>> MPI_Allreduce once
>>>> for repeated use. Previously, it calls MPI_Allreduce twice for each call
>>>> of MatGetSubMatrices_MPIAIJ().
>>>>
>>>> Hong
>>>>
>>>> ________________________________________
>>>> From: Barry Smith [[email protected]]
>>>> Sent: Friday, January 20, 2017 1:11 PM
>>>> To: Matthew Knepley
>>>> Cc: Zhang, Hong; PETSc
>>>> Subject: Re: [petsc-dev] Bug introduced in MatGetSubmatrices()
>>>>
>>>>> On Jan 20, 2017, at 12:45 PM, Matthew Knepley <[email protected]> wrote:
>>>>>
>>>>> On Fri, Jan 20, 2017 at 11:55 AM, Barry Smith <[email protected]> wrote:
>>>>>
>>>>>> On Jan 20, 2017, at 11:49 AM, Matthew Knepley <[email protected]> wrote:
>>>>>>
>>>>>> On Fri, Jan 20, 2017 at 10:49 AM, Hong <[email protected]> wrote:
>>>>>> Matt,
>>>>>> By default, the flag C->submat_singleis = false.
>>>>>> In PCSetUp_ASM(), we set it as 'true' to use
>>>>>> MatGetSubMatrices_MPIAIJ_SingleIS().
>>>>>>
>>>>>> Can you check the value of this flag in your case?
>>>>>>
>>>>>> The problem is the following:
>>>>>>
>>>>>> 1) We use MatGetSubMatrices() to extract small matrices in order to form
>>>>>> a preconditioner
>>>>>>
>>>>>> 2) We do this at each Newton iteration
>>>>>>
>>>>>> 3) We use ASM as a preconditioner for the eventual Newton solve
>>>>>>
>>>>>> 4) The second time we call MatGetSubMatrices(), it has this flag set,
>>>>>> even though we are using multiple ISes
>>>>>>
>>>>>> Solution: ALSO check that the user is in fact passing a single IS.
>>>>>>
>>>>> This requires a communication. I am confused, is the number of IS
>>>>> changing each time? If not why is the flag set?
>>>>>
>>>>> ASM sets this flag because it knows that IT is going to call
>>>>> MatGetSubMatrices() later, but it unsafe if any user calls
>>>>> MatGetSubMatrices() as well. I think overall its a fragile design and
>>>>> should be scrapped.
>>>>
>>>> You mean the user calls the SAME MatGetSubMatrices with the same
>>>> matrices, right? Not a completely different unrelated MatGetSubMatrices()
>>>> which should not be affect by the previous unrelated call.
>>>>
>>>>
>>>> Barry
>>>>
>>>>>
>>>>> Matt
>>>>>
>>>>>
>>>>> Barry
>>>>>
>>>>>> Matt
>>>>>>
>>>>>> Hong
>>>>>>
>>>>>> It comes from here:
>>>>>>
>>>>>> https://bitbucket.org/petsc/petsc/commits/c10200c1442b553b7ad65c70101560db4fa22e78
>>>>>>
>>>>>> If we ask for more than 1 matrix, it dispatches to
>>>>>>
>>>>>> MatGetSubMatrices_MPIAIJ_SingleIS()
>>>>>>
>>>>>> but then fails here
>>>>>>
>>>>>> https://bitbucket.org/petsc/petsc/annotate/2e559809f9aee9c95ee79eb0939630cfe5502c8d/src/mat/impls/aij/mpi/mpiov.c?at=master&fileviewer=file-view-default#mpiov.c-1306
>>>>>>
>>>>>> because ismax > 1. I think the ismax check needs to move up to here
>>>>>>
>>>>>> https://bitbucket.org/petsc/petsc/annotate/2e559809f9aee9c95ee79eb0939630cfe5502c8d/src/mat/impls/aij/mpi/mpiov.c?at=master&fileviewer=file-view-default#mpiov.c-2012
>>>>>>
>>>>>> but I don't know for sure. Please fix this since it is breaking PyLith.
>>>>>>
>>>>>> Matt
>>>>>>
>>>>>> --
>>>>>> 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
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> 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
>>>>
>>>>
>>>
>>>
>>>
>>>
>>> --
>>> 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
>>
>>
>>
>>
>> --
>> 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
>
>
