[openib-general] Re: [PATCH v2] [RFC] - example user mode rdma ping/pongprogram using CMA
Steve Wise
swise at opengridcomputing.com
Thu Feb 9 19:32:20 PST 2006
On Thu, 2006-02-09 at 18:42 -0800, Roland Dreier wrote:
> Steve> So what's up with these access flags on qp? You cannot set
> Steve> them on qp creation...only on qp modify. That seems
> Steve> strange. Since rdma read/writes work without these
> Steve> attributes set, I'm wondering what they really do?
>
> I'm not sure how things interact with the RDMA CM abstraction, but the
> underlying IB modify QP operation allows the QP access flags to be set
> in the RESET -> INIT state transition. A QP cannot generate or
> process any messages until it is in the INIT state (actually, until it
> is in the RTR state, which can only be reached through the INIT
> state), so there's no problem setting them early enough.
>
> RDMA operations should not work without the QP access flags set and
> I'm pretty sure that I've seen RDMAs fail without them in practice, so
> there's still a bit of a mystery with rping.
>
> - R.
After poking around, I think CMA sets these via ib_cm_init_qp_attr()
called by rdma_init_qp_attr().
Stevo.
More information about the general
mailing list