Hello, This answers some of my own questions. It seems the mirred and ifb combination is indeed what reduces performance in my case. All optimizations made to fq_codel didn't help with ingress. A simple fq_police would be a better solution for ingress than cake or fq_codel. On Sat, Feb 16, 2019 at 11:35 AM Adrian Popescu wrote: > Hello, > > On Fri, Feb 15, 2019 at 10:45 PM Dave Taht wrote: > >> 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/ > > Will this help devices with a single core CPU? > > >> >> >> * 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 >> > > The problem I deal with is performance on even lower end hardware with a > single queue. My experience with mq has been limited. > > >> >> * I really liked the ingress "skb list" rework, but I'm not sure how >> to get that from A to B. >> > > What was this skb list rework? Is there a patch somewhere? > > >> >> * 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 >> > > Ingress on its own seems to be a performance hit. Do you think this would > reduce the performance hit? > > >> >> * native codel is 32 bit, cake is 64 bit. I >> > > Was there something else you forgot to write here? > > >> >> * hashing three times as cake does is expensive. Getting a partial >> hash and combining it into a final would be faster. >> > > Could you elaborate how this would look, please? I've read the code a > while ago. It might be that I didn't figure out all the places where > hashing is done. > > >> >> * 8 way set associative is slower than 4 way and almost >> indistinguishable from 8. Even direct mapping >> > > This should be easy to address by changing the 8 ways to to 4. Was there > something else you wanted to write here? > > >> >> * 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. >> > > Perhaps further improvements made to the codel_vars struct will also help > fq_codel_fast. Do you think this could be improved further? > > A cake_fast might be worth a shot. > > >> >> 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. >> >