[Cake] overheads or rate calculation changed?

Sebastian Moeller moeller0 at gmx.de
Sat Dec 23 07:55:28 EST 2017

> On Dec 23, 2017, at 10:59, Andy Furniss <adf.lists at gmail.com> wrote:
> Sebastian Moeller wrote:
>>> qdisc cake 1: dev enp6s0 root refcnt 2 bandwidth 19690Kbit diffserv3 triple-isolate rtt 100.0ms noatm overhead 48 via-ethernet total_overhead 48 hard_header_len 14
>> 	This looks like expected, the in-kernel overhead is added to the specified overhead, just like in the past. I really really wished cake would report the packet size before and _after_ its overhead addition making sanity checking much easier. BTW tc's stab might be useful as an external check... I also wonder whether the kernel's behaviour in regards to ppp interfaces changed between kernel 4.4 and newer ones, I see the same weirdness:
> FWIW my pppoe router/pvr/nas box is running 4.1.46. It's a bay-trail dc board and they are prone to cstate bug locks, which is why I'm not running anything newer!

Thanks for saving me the experiments...

Mmh, that would indicate that dev->hard_header_len might not be the relevant variable, it might be necessary to look into the IP packets total length and the reported packet/frame size to figure out what the kernel really added (since the kernel addition should not change it might be enough to do this only for the first IP packet and cache that value).

Best Regards

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