[Cake] Lockup at high speeds

Dave Taht dave.taht at gmail.com
Sat Jun 2 14:55:50 EDT 2018

On Sat, Jun 2, 2018 at 11:21 AM, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> 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...

Am I wrong in remembering that some qdisc stats are multi-core (like qlen?), and
summed at some other step?

If you pin the card or qdisc to a single core what happens? (Besides
it getting slower)

>> 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...
> -Toke


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

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