[Cake] issue with Cake and bpf filter

Pete Heist pete at heistp.net
Wed Aug 22 05:30:25 EDT 2018

> On Aug 22, 2018, at 8:17 AM, Jonathan Morton <chromatix99 at gmail.com> wrote:
>> On 22 Aug, 2018, at 12:06 am, Pete Heist <pete at heistp.net> wrote:
>> when fq_codel is the qdisc, the eBPF action is only called "once in a while”
> One difference between fq_codel and Cake is that the former - which has no shaper - will "bypass" packets when it's empty and there's no back-pressure filling it.  In that case no packet classification occurs and filters will not be called.  Or at least, that's how it used to be set up; I haven't looked at it recently.  Cake does not rely on the same set of assumptions, so will always call the filter.

Aha, that sounds likely, I’ll try with htb and a rate limit. Testing with fq_codel was challenging as I had to “do stuff” until my printk’s were eventually called, but it’s easier now that I can use cake. I suppose in my case fq_codel’s behavior would be ok in production, because if there’s no queue then there’s no need to classify. Maybe in some other cases (like gathering stats), it could be problematic.

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