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

[Sean Hefty]

Michael S. Tsirkin wrote:
> I think that the CM flow control parameter affects the requestor.
> This option is for responder.

The CM flow control parameter indicates if the local HCA implements flow control 
or always advertises invalid credits.  It's carried in both the REQ and REP 
messages, so we end up knowing the value used by both sides.  (See 12.7.26)

The only way I can find for consumers to make use of this value is for them to 
change their algorithms based on whether flow control is supported or not.  But 
it's not clear to me how the consumer determines what value to set flow control to.

I think that we need to relate anything that we do with flow control in with the 
value exchanged as part of the IB CM protocol.  (This value is also exposed 
through the RDMA CM as well.)  From an architectural view, this may require 
changing the meaning of the value carried in the IB CM messages from 'signifying 
whether the local CA actually implements flow control', to 'signifying whether 
the local QP will implement flow control'.

- Sean