[openib-general] Re: RFC: e2e credits

[Michael S. Tsirkin]

Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > > > > > > > >Sean, just to wrap it up, the API at the verbs layer will look
> > > > > > > > >like the below, and then ULPs just put the value they want in
> > > > > > > > >the CM and CM will pass it in to low level.

So this is our question, right?


CM REQ and REP messages include the following field:

---------------
12.7.26 END-TO-END FLOW CONTROL
Signifies whether the local CA actually implements End-to-End Flow Control
(1), or instead always advertises .invalid credits.(0). See section
9.7.7.2 End-to-End (Message Level) Flow Control for more detail.
---------------

Consider and implementation that advertises valid credits for
connections, and always advertises invalid credits for other connections.
This is compliant since the IB spec says (end-to-end (message level) flow
control, Requester Behaviour):
"Even a responder which does generate end-to-end credits may choose to send the
'invalid' code in the AETH"

Is it compliant for CM implementations to set/clear the End-to-End Flow Control
field accordingly, taking it to mean

"whether the local CA actually implements End-to-End Flow Control
(1), or instead always advertises 'invalid credits'(0)"
*for the specific connection*


-- 
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies