On Feb 14, 2013, at 1:36 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> 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().
Ok, seems fine then.
Barry
>
>
> 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.
>
>
