[openib-general] RFC: detecting duplicate MAD requests

[Sean Hefty]

>> There is a real issue that is seen when a duplicate request (same TID, SGID,
>> mgmt class) is received at the client, resulting in a duplicate response.
>
>You had mentioned in the previous email on this that this was the case
>of a slow responder. Is the responder slow but playing by the IB
>timeouts in effect or is it violating those timeouts ?

I don't believe that the responder is violating any timeouts.

>> The MAD layer cannot allow the duplicate response to be sent because of RMPP
>issues.
>
>Is this different for non RMPP MADs v. RMPP MADs ? Is the RMPP issue
>what you mention below (RMPP receiving a duplicate response) ? If so, is
>this an implementation or architecture issue or both ?

The issue is a result of the RMPP architecture, but I wouldn't say that RMPP has
an issue.  It's simply a matter that you can't reassemble multiple MADs from the
same source that use the same transaction ID.

For non-RMPP MADs, the only issue is one of efficiency.  A duplicate response
would just be dropped on the requester side if the first response is received.

>> A client is still restricted from sending a duplicate response while a
>previous
>> response is in progress.  RMPP cannot handle this case.
>
>Why not ? Wouldn't the second response not match anything in the client
>on the request side ?

This is true if the first response completes before the second response is sent.
The problem is when both responses are active at the same time.

- Sean