On Mon, Nov 23, 2015 at 03:30:42PM -0800, Caitlin Bestler wrote:Is it possible for an IB HCA to transmit a response on a QP and not in that packet
The receive completion can be safely assumed to indicate transmitPerhaps iWarp is different and does specify this ordering but IB does
completion over a reliable connection unless your peer has gone
completely bonkers and is replying to a command that it did not
The issue with IB is how the ACK protocol is designed. There is not
strong ordering between ACKs and data transfers. A HCA can send
ACK,DATA and the network could drop the ACK. The recevier side does
not know the ACK was lost and goes ahead to process DATA.
Since only ACK advances the sendq and DATA advances the recvq it is
trivial to get a case where the recvq is advanced with a reply while
the sendq continues to wait for the ACK to be resent.
Further IB allows ACK coalescing and has no rules for how an ACK is
placed. It is entirely valid for a HCA to RECV,REPLY,ACK - for