[ofa-general] RDS flow control

[Richard Frank]

We should define a set of performance criteria / tests to ensure we do 
not impact our current performance with IB...

An alternative would be to push this into an IWARP specific 
module....and if works well there - we might then want to move it to 
generic RDS layer ? As an example, the TCP transport for RDS - handles 
flow control internally..

Jon Mason wrote:
> 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
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