[c-nsp] Flow Control and 10GE interfaces

[Kevin Graham]

> The answer is very simple: if someone thinks that ethernet flow

> control is the answer, the burden of proof is on them to answer
> difficult questions about what the actual problem is, what flow
> control is going to solve, and why they think that it won't cause more
> problems than its worth.  At best it does nothing, realistically it
> interferes with TCP flow control, and at worst it pauses your storage
> and breaks every client.

My understanding of this must be broken... If the pause frame is sent
only sent when or immediately before RX buffers are exhausted, then
TX queuing is triggered (hopefully only briefly before those buffers
are exhausted). This would seem to trigger behavior consistent w/ a
congested interface (which in fact it is, just prior to reaching line
rate, as the receiver can't take it off interface buffers fast enough).

Short of host-side implementation details such as one slow MSI-X queue
starving others, isn't this providing exactly the congestion feedback
that would be expected (queue-on-congestion, drop when queue
exceeded)?