> Because underlying code behaves differently based on the hop_limit
> (changes the timeout and LID values), I'd like to see the hop_limit setting at
> least take into account whether the src/dst addresses are on different
> subnets, so that it can remain 1 when routing is not in use.
> 
Just wondering if it'd scale better if we start off with a known bigger default 
hop limit and set it to 1 only if we know that we are _not_ going out of the 
subnet ?

In any case, I'm still trying to understand how best to do what you are 
suggesting i.e take into account the src/dst addresses on different subnets , 
and so far the only piece 
Of code that I could find that does something close to that would be the 
ib_init_ah_from_path() , in particular the snippet (and my comment )below.
Would you suggest modifying it here?  Is my understanding correct or am I 
missing something ?

force_grh = rdma_port_get_link_layer(device, port_num) == 
IB_LINK_LAYER_ETHERNET;

        if (rec->hop_limit > 1 || force_grh) {
        ..
        ..
        ah_attr->grh.hop_limit     = rec->hop_limit;    /* This seems to be the 
key which is why I was modifying the value in cma_resolve_iboe_route() */
        ..
        }
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