I still regard inbound shaping as our biggest deployment problem, especially on cheap hardware.
Some days I want to go back to revisiting the ideas in the "bobbie" shaper, other days... In terms of speeding up cake: * At higher speeds (e.g. > 200mbit) cake tends to bottleneck on a single cpu, in softirq. A lwn article just went by about a proposed set of improvements for that: https://lwn.net/SubscriberLink/779738/771e8f7050c26ade/ * Hardware multiqueue is more and more common (APU2 has 4). FQ_codel is inherently parallel and could take advantage of hardware multiqueue, if there was a better way to express it. What happens nowadays is you get the "mq" scheduler with 4 fq_codel instances, when running at line rate, but I tend to think with 64 hardware queues, increasingly common in the >10GigE, having 64k fq_codel queues is excessive. I'd love it if there was a way to have there be a divisor in the mq -> subqdisc code so that we would have, oh, 32 queues per hw queue in this case. Worse, there's no way to attach a global shaped instance to that hardware, e.g. in cake, which forces all those hardware queues (even across cpus) into one. The ingress mirred code, here, is also a problem. a "cake-mq" seemed feasible (basically you just turn the shaper tracking into an atomic operation in three places), but the overlying qdisc architecture for sch_mq -> subqdiscs has to be extended or bypassed, somehow. (there's no way for sch_mq to automagically pass sub-qdisc options to the next qdisc, and there's no reason to have sch_mq * I really liked the ingress "skb list" rework, but I'm not sure how to get that from A to B. * and I have a long standing dream of being able to kill off mirred entirely and just be able to write tc qdisc add dev eth0 ingress cake bandwidth X * native codel is 32 bit, cake is 64 bit. I * hashing three times as cake does is expensive. Getting a partial hash and combining it into a final would be faster. * 8 way set associative is slower than 4 way and almost indistinguishable from 8. Even direct mapping * The cake blue code is rarely triggered and inline I really did want cake to be faster than htb+fq_codel, I started a project to basically ressurrect "early cake" - which WAS 40% faster than htb+fq_codel and add in the idea *only* of an atomic builtin hw-mq shaper a while back, but haven't got back to it. https://github.com/dtaht/fq_codel_fast with everything I ripped out in that it was about 5% less cpu to start with. I can't tell you how many times I've looked over https://elixir.bootlin.com/linux/latest/source/net/sched/sch_mqprio.c hoping that enlightment would strike and there was a clean way to get rid of that layer of abstraction. But coming up with how to run more stuff in parallel was beyond my rcu-foo. _______________________________________________ Cake mailing list [email protected] https://lists.bufferbloat.net/listinfo/cake
