Brightwell, Ronald wrote:
I'm looking at a network where the number of endpoints is large enough that everybody can't have a credit to start with, and the "offender" isn't any single process, but rather a combination of processes doing N-to-1 where N is sufficiently large. I can't just tell one process to slow down. I have to tell them all to slow down and do it quickly...
When you have N->1 patterns, then the hardware flow-control will throttle the senders, or drop packets if there is no hardware flow-control. If you don't have HOL blocking but the receiver does not consume for any reasons (busy, sleeping, dead, whatever), then you can still drop packets on the receiver (NIC, driver, thread) at a last resort, this is what TCP does. The key is have exponential backoff (or a reasonably large resend timeout) to no continue the hammering.
It costs nothing in the common case (unlike the credits approach), but it does handle corner cases without affecting too much other nodes (unlike hardware flow-control).
But you know all that. You are just being mean to your users because you can :-) The sick part is that I think I envy you...
Patrick
