[Cake] tossing acks into the background queue

[Toke Høiland-Jørgensen]

Dave Taht <dave.taht at gmail.com> writes:

> On Tue, Nov 23, 2021 at 2:39 AM Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>
>> Sebastian Moeller <moeller0 at gmx.de> writes:
>>
>> > Hi Dave,
>> >
>> > On 23 November 2021 08:32:06 CET, Dave Taht <dave.taht at gmail.com> wrote:
>> >>The context of my question is basically this:
>> >>
>> >>Is cake baked? Is it done?
>> >
>> > How about per MAC address fairness (useful for ISPs and to treat
>> > IPv4/6 equally)?
>> >
>> > How about configurable number of queues (again helpful for ISPs)?
>>
>> FWIW I don't think CAKE is the right thing for ISPs, except in a
>> deployment where there's a single CAKE instance per customer. For
>> anything else (i.e., a single shaper that handles multiple customers),
>> you really need hierarchical policy enforcement like in a traditional
>> HTB configuration. And retrofitting this on top of CAKE is going to
>> conflict with the existing functionality, so it probably has to be a
>> separate qdisc anyway.
>
> What progress has been made on breaking the HTB locks in the last few
> years?

None. Don't see that happening any time soon; just the simple pfifo_fast
qdisc is uncovering all kinds of bugs when running in lockless mode.

Jesper basically solved the contention issue by partitioning the traffic
and running multiple instances:
https://github.com/xdp-project/xdp-cpumap-tc

Doesn't work for bandwidth sharing across instances, though, so it
solves the ISP "separate rates per customer" case, but not the CAKE
"shape a single link" case.

> Given the enormous number of hw tx/rx queues we see today (64+ on
> 10gbit), trying to charge off
> bandwidth per queue in a cake-derived shaper and protecting the merge
> with rcu seemed plausible...

Yeah, that was what I was going to try, but it turned out to be
decidedly non-trivial to make sch_cake itself mq-aware, so I gave up. My
hope is that this will be possible once we get sch_bpf, so we can just
have separate instances but they can share a single atomic var for the
bandwidth sync...

-Toke