[petsc-dev] MPIX_Iallreduce()

[Barry Smith]

  Add a glance adding all these new complications to PETSc to chase an impossible overlap of communication and computation sounds fine :-)

   Barry

  Just nice clean uncomplicated code please :-)


On Mar 18, 2012, at 11:29 AM, Jed Brown wrote:

> On Sun, Mar 18, 2012 at 11:24, Matthew Knepley <knepley at gmail.com> wrote:
> This sounds fine to me. I think the acid test is to rewrite Bill's new CG in it.
> 
> Someone at ICERM knew the reference for that, right?
>  
> 
> I do not understand this. What call creates the PetscSplitReduction struct?
> 
> PetscSplitReductionGet(MPI_Comm) gets it out of the attribute cache on the comm, creating it if it doesn't exist yet.
>  
> Is it the Begins? So after Begin, it is present in
> the Vec and the Comm.
> 
> Currently only in the Comm, and it's always accessed the same way.
>  
> Then when you call PetscCommSplitReductionBegin, it leaves the comm, and resides only in the
> Vec along with a Request. Then the End destroys it? So it lives in the Comm for aggregation purposes? That sounds fine to
> me.
> 
> Right, I want it to still live in the comm for aggregation purposes, but have a reference count and have the link from the comm dropped when the reduction starts.