Re: How to know if SRQ is being used in SRP?

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

  > I have the envious task of figuring out whether SRQ is being used in
  > an SRP application (which I have very little knowledge about). I
  > only have IB transport layer traces from the customer.  From the
  > traces I can see Valid Credits in the Syndrome field of the AETH in
  > RDMA_ReadResponse_First/last messages.  Although there are a bunch
  > of RC SENDs where the AETH syndrome field is Invalid, unfortunately
  > I cannot seem to correlate these RC SENDS with the RDMA
  > read/responses.  My questions is, since the RDMA response AETH field
  > has valid CC credits is it saying SRQ is not being used?

As I guess you know, if end-to-end credits are used on an RC connection,
then SRQ cannot be used on that connection.  The opposite implication
does not hold: eg a TCA might not implement the optional end-to-end flow
control protocol, and hence a non-SRQ connection might still not use
end-to-end flow control.

Also end-to-end flow control is negotiated for each direction of a
connection independently, so you might see valid end-to-end credits sent
in only one direction.

Essentially the only thing you can learn from a wire-level trace is the
following: if you see an AETH with valid end-to-end credits being sent
from CA X, then the corresponding receive queue on CA X is not attached
to an SRQ.  I don't believe there is anything further you can deduce.
(Certainly invalid end-to-end credits do not imply that an SRQ is being
used, they simply imply that the end-to-end flow control protocol is not
in use)

 - R.
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Roland Dreier <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> || For corporate legal information go to:
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