[Cake] cake byte limits too high by 10x

[Dave Taht <dave.taht@gmail.com>]

at 100Mbit we had 5 megabytes of max queuing. I don't think this was
jonathon's intent, as the default if no rate was specified was 1Mbyte.

Even what i did below is kind of wrong, but it did have satisfying
results for kicking in the cake ecn overload and-switch-to-drop
behavior, and stomping on slow start before it got too out of hand.

tcp's behavior is quadratic to the buffering... (it is too late at
night for me to think harder on that), and a queue is there to absorb
bursts (and also too late to think on this)

anywhy, here so we end up at 100mbit at ~340 full size packets max
with byte limits, and about 2000 acks. Compare this to the packet
limits in the sqm system (800), which were developed primarily against
testing against 5-50Mbit workloads.  On the one hand I have hope we
can always use less memory with a byte queue limited qdisc system
while still preserving good reverse direction performance. (yea! makes
for saner small router behavior) On the other hand codel does not
react fast enough to major bursts without engaging the out of
bufferspace cake_drop which is pretty darn cpu intensive. On the
gripping hand there becomes no right outer limit for a wildly variable
802.11ac wifi queue, with speeds from one to 1.5Gbit, but I sure would
like a cake-mq that handled the existing queues right with less
memory.

        if(q->rate_bps)
        {
                u64 t = q->rate_bps * q->classes[0].cparams.interval;
                do_div(t, NSEC_PER_SEC * 10 / 4);
                                                         ^^^^ added the *10
                q->buffer_limit = t;

                if(q->buffer_limit < 131072)
                        q->buffer_limit = 131072; // 64k too low a lower bound
        } else {
                q->buffer_limit = 1 << 20;
        }

        printk(KERN_WARNING "cake buffer_limit: %d", q->buffer_limit);


-- 
Dave Täht
Open Networking needs **Open Source Hardware**

https://plus.google.com/u/0/+EricRaymond/posts/JqxCe2pFr67