[mpich-discuss] MPI_Rsend advantage

[Atchley, Scott]

If you can guarantee that it is posted, then you can guarantee that it will match. If you cannot guarantee that it is posted and will match, then it may be placed in the unexpected buffer and will need to be copied into the final location once the receive is posted.

My question is, “How do you know it has been posted?”


> On Sep 6, 2017, at 6:21 AM, Dorier, Matthieu <mdorier at anl.gov> wrote:
> 
> Hi,
> 
> Out of curiosity, what gain is there to using MPI_Rsend instead of MPI_Send when I know that the receiver has posted a receive? Do I avoid a rendez-vous protocol? Do I avoid a buffer copy somewhere?
> 
> Thanks,
> 
> Matthieu
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