On Tue, 24 May 2005, Roland Dreier wrote: > Vivek> I should say it depends. One can utilise a setup that sets > Vivek> the MTU to 2044 or whatever is the UD MTU on the subnet for > Vivek> all modes. The connection will advertise the maximum > Vivek> receive MTU as this value. > > OK, but that's throwing away the main advantage of connected mode > IPoIB, right?
I was addressing the case of a minimal implementation. For sucn an an initial implementation one can go as above. However, as I noted in the previous mail, if a large MTU is to be supported then one has to split the CM and UD MTUs since the UD MTU is limited to 2 or 4K. It is the limitation of the media that we get large MTU with connected mode whereas we get multicast (absolutely necessary for for address resolution) only with UD unless we want to do multicast emulation. > > For full connected mode support, do you see an alternative to handling > per-destination MTUs? ..how about the following: To send a node must be aware of the remote node's maximum MTU. The the node can determine the minimum of these maximums. Therefore, one can go with a two way split -- for UD use the UD MTU. For any RC communication use this minimum (or less depending on the packet size). Therfore, one can decrement the RC MTU if needed at every new RC connection that is made - i.e. one does recognise the receive MTU from the peer but uses it to decrement the overall RC MTU if required. It will not be optimal for all cases since some could do with larger MTU but will interoperate. One can also administratively set a large enough 'minimum RC MTU' on all the nodes in the subnet. Vivek > > - R. > > _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
