Hi Sean,
I'm experimenting XRC with a real application and I want to share my
thoughts.
A natural way to pass the SRQ's QPN is to use the "private_data" of the
"rdma_conn_param", however this area is limited to 56 octets and since
each QPN occupies 3 octets that leaves us with 18 SRQ. I suggest to
increase the size of the private data, or to find a more convenient way
to pass the SRQ's QPM, one that doesn't use extra ports or out-of-band
communication (socket).
Another issue is of backwards compatibility of applications. Assume an
application uses a well known port, and want to allow both new XRC
enabled clients and old RC clients. It seems that this is possible using
the "rdma_create_ep" API with appropriate "rdma_addrinfo" one that
"rdma_getaddrinfo" resolved with QP type "IBV_QPT_XRC_RECV" and one with
"IBV_QPT_RC" one the same port (I hope this is allowed). A client on the
other side will first try to connect to the XRC and if it fails will
fall-back to RC.
However, a server usually uses "rdma_create_id" to associate an event
handler with an id and then bind the id to an address, and accept
connection requests asynchronously, but with these API, AFAIK there is
no way to pass the required hints.
I assume I can use the "private_data" of the "rdma_conn_param" to
distinguish between XRC enabled clients and servers and old ones, but it
doesn't seems clean, as it is implicit and not explicit.
Best regards,
S.P.
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