[petsc-dev] always calling MPI_Init_thread?

[Barry Smith]

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.
> 
>