Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

Subject: Re: [OMPI users] More on AlltoAll
From: Terry Frankcombe (terry_at_[hidden])
Date: 2008-03-20 19:58:20

If the data distribution was sufficiently predictable and long-lived
through the life of the application, could one not define new
communicators to clean up the calls?

> After reading the previous discussion on AllReduce and AlltoAll, I
> thought I would ask my question. I have a case where I have data
> unevenly distributed among the processes (unevenly means that the
> processes have differing amounts of data) that I need to globally
> redistribute, resulting in a different uneven distribution. Writing the
> code to do the redistribution using AlltoAll is straightforward.
> The problem though is that there are often special cases where each
> process only needs to exchange data with it neighbors. So the question
> is that when two processors don't have data to exchange, is the OpenMPI
> AlltoAll is written in such a way so that they don't do any
> communication? Will the AlltoAll be as efficient (or at least nearly as
> efficient) as direct send/recv among neighbors?
> Thanks!
> Dave
> _______________________________________________
> users mailing list
> users_at_[hidden]