[Cake] Lockup at high speeds

Toke Høiland-Jørgensen toke at toke.dk
Sat Jun 2 14:21:22 EDT 2018

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

> How on earth are you getting these speeds? I'm stuck at a pathetic *4*
> gbit here on the admittedly ancient 12 core boxes I'd got.
> (I'll go rework my veth topology)

Well, having actual hardware do the packet forwarding, and only having
each machine process each packet once probably helps...

> rcu stuff makes me nervous, what happens if that nat stuff is disabled entirely.
> What if you made q.len and sparse/bullk flow counts atomic ops?

The whole qdisc dequeue op is running while holding a global lock. The
freezes I'm seeing are happening because the other cores get stuck
waiting for the cake dequeue operation to complete (and thus release the
qdisc lock). Which is why I suspect an infinite loop somewhere...

> I tend to lean towards an overflow post 40gbit also.

An overflow of what? 40 Gbps is 5 GBps, which is the unit that rates are
being measured in. So there's no obvious reason to expect that... Which
is not to say it couldn't happen, of course...


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