[petsc-dev] always calling MPI_Init_thread?

[Jed Brown]

On Thu, Feb 14, 2013 at 1:25 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>
>    My concern was if a bad implementation always did some terrible thing
> with locks (even if only one thread would ever exist) thus hurting
> performance.
>
>    Is there no way to just tell MPI there ARE and WILL be no threads?
>

Yeah, MPI_THREAD_SINGLE, but there is nothing to lock when using
MPI_THREAD_FUNNELED. I figure that if the user intends to make calls from
threads, they should call MPI_Init before PetscInitialize().


>
>    Barry
>
> On Feb 14, 2013, at 1:22 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
> > On Thu, Feb 14, 2013 at 1:16 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >
> >    Do we really ALWAYS want to call this version even if we are not
> monkeying with threads at ALL?
> >
> >     Thanks
> >
> >    Barry
> >
> >  ierr = MPI_Initialized(&flag);CHKERRQ(ierr);
> >   if (!flag) {
> >     if (PETSC_COMM_WORLD != MPI_COMM_NULL)
> SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"You cannot set PETSC_COMM_WORLD if
> you have not initialized MPI first");
> > #if defined(PETSC_HAVE_MPI_INIT_THREAD)
> >     {
> >       PetscMPIInt provided;
> >       ierr =
> MPI_Init_thread(argc,args,MPI_THREAD_FUNNELED,&provided);CHKERRQ(ierr);
> >     }
> > #else
> >     ierr = MPI_Init(argc,args);CHKERRQ(ierr);
> >
> > The implementation of MPI_Init just probes around the environment and
> calls MPI_Init_thread. There is no performance advantage of
> MPI_THREAD_SINGLE over MPI_THREAD_FUNNELED so I think the code here is fine.
>
>
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