On 9/29/12 2:29 AM, "Justin YUAN SHI" <[email protected]> wrote:
>I missed this thread. Got busy with classes. Sorry. > >Going back to Jim's comments on Infiniband and OSI and MPI. I see the >exacscale computing requires us to rethink MPI's insistence on sending >message directly. Even with the group communicators, the >implementation >insists on the same. > >The problem with direct communication is that you leave the >application without a recourse when the transmission fails. As we have >discussed, any transient fault can cause that to happen. It is >practically impossible to provide redundancy for every transmission >unless we change our API design that eliminates the reliable >communication assumption. The application-level re-transmission will >allow the application to survive NOT only the communication failures >but also node failures (when you loose a chunk of memory). But the MPI >semantics does not allow this to happen, even if the implementation >tries to re-transmit a failed message. So what you're thinking is that the conceptual message passing be more like UDP sockets? That we explicitly accept that a "send" might not work, and in fact, may "fail silently". Yes.. That is a key aspect, and the higher level algorithm that uses it needs to explicitly account for it: by multiple transmissions, multiple paths, coding (in the ECC sense) or something else. _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
