[Cake] UDP floods and taking advantage of egress signalling at ingress

Dave Taht dave.taht at gmail.com
Fri May 6 03:38:59 EDT 2016

On Fri, May 6, 2016 at 12:29 AM, Kevin Darbyshire-Bryant
<kevin at darbyshire-bryant.me.uk> wrote:
> Hi All,
> My brain woke up with this idea rattling around in it this
> morning...obviously the subconscious has been busy.  So here it is:
> Is there any way to use the egress drop signalling at ingress time to drop
> stuff before it gets into the queue so then we don't have to drop it at
> egress?
> Something like: At enqueue if we've a matching flow check to see if that
> flow had been in egress 'fast dropping' state *and* know how much data in
> terms of time it had to fast drop to get the queue back under the nominal
> time threshold.  If say it had to drop 10ms worth of packets to get back to
> the nominal 5ms threshold then it dropped 67% of the packets/data.  I'd like
> to think of that as an 'unresponsive flow'...hence could it be possible to
> use that information at ingress time and in essence drop (some? 66%?) of
> them there, we can also signal congestion to the stack at that point to
> (cake already does this signalling when getting to its buffer size limit)
> Probably a very silly idea.

No, actualy, I'd been thinking about the same thing myself for days.
:) I've always wanted a way to notify userspace that I was dropping
(the heck out of) something on egress to try and stuff it up on
ingress, or do something more intelligent like re-route the traffic

There was a lot of talk about adding the ability to drop stuff really
fast in the rx ring recently using the jit BPF stuff.

I was at a meeting where tom herbert talked about that, and I confess,
extremely dubious. Then... well, I see lots of drops on ingress
already I don't want, the udp flooding episode made me go look harder
at whole system behavior...

and I can't find the lwn article about it.

> --
> Thanks,
> Kevin at Darbyshire-Bryant.me.uk
> M: +44 7947 355344 H: +44 1256 478597
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Dave Täht
Let's go make home routers and wifi faster! With better software!

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