[Cake] Long-RTT broken again

Toke Høiland-Jørgensen toke at toke.dk
Tue Nov 3 06:57:50 EST 2015

Sebastian Moeller <moeller0 at gmx.de> writes:

> Well, I believe one of the next steps needs to be to expose limit to
> user-space,

No, just throwing the problem to user space is not a solution: it's a
cop-out. We need to fix the issues so things actually work, and then
*maybe* expose the value to userspace if there is a real need for it.
Not just go "meh, let userspace sort it out"; that is horrible design.

> which would have Toke allowed his measurements

No, it would not: I'm not trying to test whether we have a qdisc that,
through arcane configuration options, can be made to behave properly.
That already exists in fq_codel+HTB. What we're doing here is trying to
build a no-knobs qdisc here that works well in all the scenarios we can
think of. So let's make sure it does, and then talk about whether a
variable should be exposed *after* we've done proper auto-tuning.

> and would have followed the example of most/all other leaf qdiscs and
> put policy into user space where it arguably belongs…

Packet limit is not policy, it's an implementation detail. If you don't
have the memory to run at 100Mbps / 1 second, then *set those values
lower*. You're not going to achieve it anyway if you don't have the
buffer space.

Same thing with the target parameter, BTW: The fact that we still
haven't got it right is not an argument for exposing it to userspace,
quite the contrary: If we, the experts, can't even get it right, why on
earth would be expect users to?


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