[Mpi-22] [Mpi-forum] MPI 2.2 proposal:resolving MPI_Request_free issues

[Jeff Squyres]

On Jul 16, 2008, at 7:31 PM, Underwood, Keith D wrote:

>>> [erezh] Correct; this is the scenario I was describing with the RDMA
> write.
>
> It would be interesting to see exactly what the error mode here is.
> Retransmitting corrupted data should be ok, since a correctly  
> delivered
> message means that the retransmit must be dropped.  I suppose that if
> the NIC speaks virtual addresses and the free actually results in a  
> trap
> to the kernel that unmaps the pages, then the NIC could retransmit and
> find that there isn't a valid page table entry...

'zactly.  And then the local completion entry would be a failure -- so  
the sender would [erroneously] think that the message had failed to be  
delivered.

> Solution #5:  Change the advice to users - "...the arrival of the  
> reply
> informs the sender that the send has completed and the send buffer can
> be overwritten.  If the buffer will ever be freed, the application
> should call MPI_Wait or MPI_Cancel instead of MPI_Request_free."

That seems like a good compromise.


-- 
Jeff Squyres
Cisco Systems