[Cake] pie in dd-wrt

Toke Høiland-Jørgensen toke at redhat.com
Wed Aug 21 17:40:41 EDT 2019

Dave Taht <dave at taht.net> writes:

> Sebastian Gottschall <s.gottschall at newmedia-net.de> writes:
>> Am 21.08.2019 um 18:21 schrieb Sebastian Moeller:
>>> On August 21, 2019 6:12:03 PM GMT+02:00, Sebastian Gottschall <s.gottschall at newmedia-net.de> wrote:
>>>> thats rather old. i rewrote all the qos code in the last 4 or 5 days.
>>>> so
>>>> things might be changed. next phase is bringing all the link level
>>>> detail configuration stuff into the gui which will be done
>>>> tomorrow or at least still within this week.
>>>> i also added now cake to some smaller low budged routers with limited
>>>> resources, so see how it runs. i had bad experiences with fq_codel in
>>>> the past due some high memory usage.
>>>> especially since its hard coded somewhat into the wireless ath9k
>>>> driver.
>>>> so i already modded it for more efficient handling. 4 mb max per queue
>>>> is simply too much for  a 32 mb ram based router.
>>> This is why I'm sqm we reduced the queued packet maximum m to around 1000, and also why cake has an explicit memlimit keyword.
>> yeah but does this help if fq_codel is hardcoded into mac80211?
>> fq_codel has a memlimit  keyword too btw. its fixed to 4MB. i reduced
>> it to 256kb on low memory architectures. no other way to get around
>> OOM problems
>> mac80211  does always make use of fq_codel. it has a own build in
>> implementation
> Certainly memory limits are a huge problem throughout complex qdiscs,
> especially when stacked up (eg hfsc 1 -> qdiscx hfsc 2 -> qdisc x),
> and 
> OOMs suck. Particularly as few test packet flooding their devices
> after setting up a complex qdisc system. 
> Bytes = time. It doesn't matter how many queues you have. This
> to me has always been one of the biggest flaws of the tc subsystem
> in general is that the total amount of memory in use on
> a given physical interface should be managed by the topmost layer.
> Same problem for wifi in multiple SSIDs... it's still just one device.
> However we do need enough bytes to keep the device busy and there
> are other problems with per packet limits leading me to prefer
> using just memory limits. One is, that your typical ack packet
> coming off the rx ring is actually 2k in size, not 64 bytes.
> I had at one point (in openwrt) something that took small packets
> and copied them to a smaller allocation which took pressure off the
> memory allocator.
> I've kind of lost track, did the ath9k wifi stuff use 1 allocation for
> all 4 hw queues? I'm afraid to look this morning... (and I'm not big
> on the 4 hw queues either)

The memory limit in mac80211 is global per phy.


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