[Beowulf] MPI Persistent Comm Question

Mark Hahn hahn at mcmaster.ca
Mon Jun 28 15:40:26 EDT 2010


> Uhmmm, what is "MPI_Free()"?

he probably meant MPI_Request_free

> (1)
> Call this subroutines 1000 times
> =============================
>             call MPI_RECV_Init()
>             call MPI_Send_Init()
>             call MPI_Startall()
>             call MPI_Free()
> =============================
>
> (2)
> Call this subroutines 1000 times
> ===========================
>             call MPI_RECV_Init()
>             call MPI_Send_Init()
>             call MPI_Startall()
> ==========================
>            call MPI_Free()  --------- call it only once at the end.

I've never even seen these MPI_Start-related interfaces in use, 
but MPI_Request_free appears to be callable once per MPI_*_Init.
that would argue for pairing as in the first sequence.

afaikt, the point of the interface is actually init/start+/free - 
that is, you set up a persistent send and kick it into action 
many times.  but only free it once.
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