[ofa-general] detecting "recv buffer not available" events

[James Lentini]

On Tue, 4 Mar 2008, Steve Wise wrote:

> All,
> 
> This question is regarding SENDs arriving when no RECV buffer is 
> posted.  For IB, somehow the transport can deal with this and force 
> the sender transport to retransmit.
> 
> First, is my statement above correct?

This is correct for IB's RC and RD transports.

The IBTA spec has more info (see RNR retry and RNR timer).

The struct ib_qp_attr's min_rnr_timer and rnr_retry fields allow fine 
grained control of these values (rnr_retry == 7 means infinite).

ULPs generaly interact with these values through either the IB CM's 
struct ib_cm_req_param/struct ib_cm_rep_param (if the ULP is IB 
specific) or the RDMA CM's struct rdma_conn_param.

> If so, How can I detect that this is happening on an IB RC?  IE is 
> there some stat I can query?

Good question. I don't see an obvious stat in /sys/class/infiniband.