[ofa-general] Re: Has anyone tried running RDS over 10GE / IWARP NICs ?

[Steve Wise]

Richard Frank wrote:
> Hmmm - so what happens with IWARP NIC when no buffer is posted on recv q 
> and a message arrives ?
> 
> 

The spec sez the implementation can terminate the connection.  That is 
exactly what ammasso and chelsio's rnics do.  The spec doesn't mandate 
this behavior however.  So an incoming SEND could to be dropped and not 
ack'd at the TCP level forcing the client to retransmit.  But I don't 
know of an rnic that does this.

FYI: The reason the rnic implementation might terminate in this case is 
due to the protocol stack layering.  If the rdma layers (mpa, ddp, 
rdmap) sitting on top of TCP don't tell TCP when to ack something, then 
the incoming SEND might be acked by TCP before the RDMA layers process 
the packet.  Then the SEND cannot be dropped since its already acked. 
So the message either must be buffered until the RECV is posted, or the 
connection terminated.


Steve.