[petsc-users] Should I synchronize processes explicitly, for instance using MPI_Barrier?

[Cong Li]

Hi, Matthew
Thank you very much for the answer.

And I met a new problem.
When there some PetscScalar type data operations before the VecWAXPY call,
for example

PetscScalar, a,b, c;
.....
.....
c=a+b;
ierr = VecWAXPY(r, c, Ax, b);CHKERRQ(ierr);

, should I add MPI_Barrier call right before VecWAXPY call ?

Best regards

Cong


On Fri, Aug 16, 2013 at 7:56 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Fri, Aug 16, 2013 at 2:11 AM, Cong Li <solvercorleone at gmail.com> wrote:
>
>> Hi
>>
>> I am a rookie to PETSc, and I am wondering about whether I should call
>> MPI_Barrier to explicitly synchronize processes between PETSc calls.
>> For example, a piece of code like below
>>
>>   ierr = MatMult(A,x,Ax); CHKERRQ(ierr);
>>   ierr = VecWAXPY(r, neg_one, Ax, b);CHKERRQ(ierr);
>>
>> Should I add MPI_Barrier inbetween MatMult call and VecWAXPY call ?
>>
>
> No
>
>    Matt
>
>
>> My guess is that it is unnecessary. However, I am not so confident in
>> this guess, for I don't have much experience on using PETSc.
>>
>> Thanks in advance.
>>
>> Cong Li
>>
>
>
>
> --
> 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
>
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