[openib-general] Immediate data question

[Michael Krause]

At 03:41 PM 2/7/2007, Roland Dreier wrote:
>     Changqing> What I mean is that, is there any performance penalty
>     Changqing> for receiver's overall performance if RNR happens
>     Changqing> continuously on one of the QP ?
>
>Not for the receiver, but the sender will be severely slowed down by
>having to wait for the RNR timeouts.

RNR = Receiver Not Ready so by definition, the data flow isn't going to 
progress until the receiver is ready to receive data.   If a receive QP 
enters RNR for a RC, then it is likely not progressing as desired.   RNR 
was initially put in place to enable a receiver to create back pressure to 
the sender without causing a fatal error condition.  It should rarely be 
entered and therefore should have negligible impact on overall performance 
however when a RNR occurs, no forward progress will occur so performance is 
essentially zero.

Mike