[openib-general] Re: Re: RFC: e2e credits

[Michael S. Tsirkin]

Quoting r. Sean Hefty <sean.hefty at intel.com>:
> Subject: RE: Re: RFC: e2e credits
> 
> >> So, how about we add a flag to ib_qp_init_attr?
> >> Something like
> >> 	responder_invalid_credits
> >> 
> >> Which will, for RC QPs, cause the responder to always
> >> generate invalid credits, effectively disabling hardware E2E
> >> flow control for this receive queue.  ULPs will turn this on
> >> if they do implement flow control in software and make sure that RNR
> >> is never generated. 
> 
> At first glance, this sounds reasonable.  This could end up breaking the
> ABI somewhere (verbs, CM, CMA?), but I'm not sure.  How does this map to
> the IB CM flow control parameter?  (I'm at a traveler's PC at the
> moment, and don't have access to the specs.)  Is the IB CM flow control
> parameter actually used anywhere, or just exchanged by the remote sides?

What does the flow_control parameter in ib_cm and rdma_cma conn_param do?
If that's what it is, I think its easier to just add API to ib verbs
making it possible to implement it than invent a device-specific way
to do it per driver.

-- 
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies