Re: [PATCH] drivers/rxe: improve rxe loopback

[Moni Shoua]

>> Have you considered using ip_route_output_key() for IPv4 or
>> ip6_route_output() for IPv6 to decide if  this is a loopback?
>> For reference you can check the flow starting at  rdma_resolve_ip()
>>
>
> Hi Moni,
>
> Yes, I had looked into it, but I haven't seen how I can find
> out if the destination IP belongs to the same RXE.
> The loopback flag will give us the "same host"
> confirmation, but not the same rxe instance, right?
>
> Any ideas would be welcomed.
>
> Thanks,
> Marcel
>
Hi Marcel

You are right about that. IFF_LOOPBACK tells you that the source and
destination addresses are on the same host but not necessarily on the
same RXE device.

As Leon mentioned, calling addrX_same_rxe() for each packet seems to
heavy , especially when the use case that justifies it (instead of
calling memcmp() on src and dst) is rare. Do you agree?
If so I think that marking a connection as loopback once is the right approach
For RC/UC - when modified to RTR
For UD - this is harder. IsLoopback() is function of the WQE (or at
least the QP and AH together( but not the QP. I think you can add an
improvement that will work for the majority of cases. This is a sketch
of what I have in mind. Let me know what you think please

1. Add bool last_used_qp to AH structure
2. Add bool is_loopback_with_last_qp to AH structure
3. Set values to AH.last_used_qp and AH.is_loopback_with_last_qp in
post_send() modify_ah(),...
4. Mark WQE as loopback depending on the above