Jonathan, I think this would be a great idea to implement and test. Can COBALT's behavior be easily implemented to test it using the OpenWRT or LEVE ?
Regards, Luis On Fri, May 20, 2016 at 8:36 AM, Jonathan Morton <chromati...@gmail.com> wrote: > >> If the relative load from the flow decreases, BLUE’s action will begin > to leave the subqueue empty when serviced, causing BLUE’s drop probability > to fall off gradually, potentially until it reaches zero. At this point > the subqueue is naturally reset and will react normally to subsequent > traffic using it. > > > > But if we reach a queue length of codel’s target (for some small amount > of time), would that not be the best point in time to hand back to codel? > Otherwise we push the queue to zero only to have codel come in and let it > grow back to target (well approximately). > > No, because at that moment we can only assume that it is the heavy > pressure of BLUE that is keeping the queue under control. Again, this is > an aspect of Codel’s behaviour which should not be duplicated in its > alternate, because it depends on assumptions which have been demonstrated > not to hold. > > BLUE doesn’t even start backing off until it sees the queue empty, so for > the simple and common case of an isochronous flow (or a steady flood > limited by some upstream capacity), BLUE will rapidly increase its drop > rate until the queue stops being continuously full. In all likelihood the > queue will now slowly and steadily drain until it is empty. But the load > is still there, so if BLUE stopped dropping entirely at that point, the > queue would almost instantly be full again and it would have to ramp up > from scratch. > > Instead, BLUE backs off slightly and waits to see if the queue *remains* > empty during its timeout. If so, it backs off some more. As long as the > queue is still serviced while BLUE’s drop probability is nonzero, it will > back down all the way to zero *if* the traffic has really gone away or > become responsive enough for Codel to deal with. > > Hence BLUE will hand control back to Codel only when it is sure its extra > effort is not required. > > - Jonathan Morton > > _______________________________________________ > Cake mailing list > Cake@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/cake >
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