[ofa-general] RDS flow control

[Jon Mason]

As part of my effort to get RDS working for iWARP, I will be working on the 
RDS flow control.  Flow control is needed for iWARP due to the fact that 
iWARP connections terminate if there is no posted recv for an incoming 
packet.  IB connections do not have this limitation if setup in a certain 
way.  In its current implementation, RDS sets the connection attribute 
rnr_retry to 7.  This causes IB to retransmit until there is a posted recv 
buffer. 

Using a credit based flow control mechanism, we can ensure there will be a 
posted recv for every incoming packet (thus laying part of the foundation of 
allowing iWARP to work).  Also, it will reduce unnecessary IB transport 
traffic (at the expense of maintaining the credit schema).

I am still in the very early stages of implementing this.  So any pointers to 
RDS documentation (or a RDS git tree) would be very helpful.  I have a small 
IB setup to test this on, so anyone willing to test it when I am done would 
be helpful as well.

Thanks,
Jon