[Cake] cake at 60gbit

Pete Heist pete at heistp.net
Fri Jul 6 07:58:48 EDT 2018

> On Jul 6, 2018, at 1:33 PM, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> AHA! Found the culprit!
> The bulk dequeue mechanism in sch_generic.c will dequeue a bunch of
> packets at once, then check if they belong on the same hardware txq. If
> they don't, they will be put back on a separate queue in the qdisc
> structure (sch->skb_bad_txq), and the qlen will be increased, without
> telling the qdisc about it.

Solid, nice work!

> This obviously only happens on hardware with multiple TXQs, which is why
> the bug doesn't happen on veth.

It would be nice if veth were mq capable.

For whatever reason, I didn’t see this on my i210at’s (1gbit ethernet with 4 transmit and 4 receive queues).

I’m now playing with netem, cake and veth for the first time (two namespaces with netem as the parent qdisc to cake for each namespace). I’ve gotten the setup not to lock up in an infinite loop but to occasionally stop passing traffic sometimes after a netperf test. This could easily be a problem specific to netns though, so I’ll be playing with it some more and will post if I can narrow it down to something specific.

More information about the Cake mailing list