[ofa-general] [PATCH RFC v3 1/2] RDMA/Core: MEM_MGT_EXTENSIONS support

[Roland Dreier]

 > The "invalidate local stag" part of a read is just a local sink side
 > operation (ie no wire protocol change from a read).  It's not like
 > processing an ingress send-with-inv.  It is really functionally like a
 > read followed immediately by a fenced invalidate-local, but it doesn't
 > stall the pipe.  So the device has to remember the read is a "with inv
 > local stag" and invalidate the stag after the read response is placed
 > and before the WCE is reaped by the application.

Yes, understood.  My point was just that in IB, at least in theory, one
could just use an L_Key that doesn't have any remote permissions in the
scatter list of an RDMA read, while in iWARP, the STag used to place an
RDMA read response has to have remote write permission.  So RDMA read
with invalidate makes sense for iWARP, because it gives a race-free way
to allow an STag to be invalidated immediately after an RDMA read
response is placed, while in IB it's simpler just to never give remote
access at all.

 - R.