[ofa-general] IB credit-based flow control

[Andy Grover]

Sean Hefty wrote:
> My assumption is that if no credits are available when the SEND request arrives,
> then the receiver generates a RNR message, but I didn't read through the entire
> section to verify this.
> 
> This is totally a guess, but there needs to be some sort of recovery mechanism
> in place to handle a lost credit update message.  Allowing the requester to
> issue a limited request in the absence of credits will force a credit update if
> any are available.
> 
> Did you verify that the HCAs you're using implement e2e flow control?

How would I verify that? I'm using current HCAs (mlx4), so I'm assuming 
if the spec says an HCA must support something, is is supported?

We definitely still need ulp-level flow control for iwarp so it's not 
wasted work. But if IB doesn't, then it would be great to not incur the 
overhead.

Thanks -- Regards -- Andy