RE: [PATCH rdma-next 0/3] Support out of order data placement

["Steve Wise" <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

> > > When transmitter and receiver is enabled to do so, as I described in
> > overview section of Documentation, it helps
> > > (a) to avoid retransmission - improves network utilization
> > > (b) reduces latency due to timers not kicking in.
> >
> > Yes those benefits are clear. I see no reason why it shouldn't always
> > be
> > done is my point. Application shouldn't have to care and there is no
> > need to make this an additional flag.
> 
> The app cares when data from write 2 can be written at the target before data
> from write 1, especially if the writes target the same memory buffers.  (At least I
> think this is the intent of exposing this to the app.)
> 
> Note that the provider can always provide stronger ordering than what the app
> needs.

My understanding is that IB or IW apps should never assume ingress write or read response data is _placed_ into local memory in the order it was transmitted from the peer.  The only guarantee is that the _indication_ of the arrived data preserve the sender's ordering.  However, I'm thinking that there are applications out there that spin polling local memory that is the target of a write or read response and assume the last bit of that memory will get written last...

 

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