SQM bufferbloat


I’m using a zyxel router in bridge mode and a BT router with openwrt on it with the latest version. However I’m struggling to get good bufferbloat with SqM I’m not sure why as I get full A+ with edge router X and netduma R2, I’ve checked everything I can do but not sure what I’m missing.

Hope you guys can guide me …


SQM settings? CPU saturation? Need details to help you.

Cake, Piece of cake, PPPoE, factory reset only has SqM on it, Sorry I’m new to openwrt so go gentle on me :blush::joy:

It's not even clear yet what device you're using for sqm (apart from ZyXEL veing a vendor with thousands of different devices, not a specific model), nor what WAN speed we're talking about.

Well, have you read the SQM documentation, here and here already?
If you have not, that would be a good starting point :wink:

That said, could you post the following information:

  1. ISP name, and pln speed (upload and download)

  2. output of the following commands run on a ssh shell on your OpenWrt router:

a) get the name of the wan device/interface: ifstatus wan | grep device
b) get the current configuration of cat /etc/config/sqm
c) disable sqm: /etc/init.d/sqm stop
d) run a dslreports speedtest with SQM disabled and post the results here
e) enable SQM (copy and paste the output here in formatted as </> preformatted text): SQM_DEBUG=1 SQM_VERBOSITY_MAX=8 /etc/init.d/sqm start
f) get the initial cake statistics: tc -s qdisc
g) run another dslreports speedtest and post a link to the detailed results here.
h) get the post-speedtest cake statstics: tc -s qdisc

That should get us in a decent position to continue the discussion/optimization of your SQM configuration.


All sorted now, Thanks for your help sorry I wasn't helping to much on giving you more information but I'm new to openwrt :slight_smile:

How can I get open nat on the xbox s?

Great to hear. What was the solution (if you are willing to post it here, other's might learn from your experience if they stumble over this thread)?

Sorry, not my area of expertise, but I am sure there are people on this forum who know.

The measured speed was in Kbit/s not mbps, So got a little confused, Also which one is my WAN connection> etho.2 or pppoe-VDSL? so I can set it correctly on the SqM page



Also I have a 80/20 speed FTTC, I need to set my SqM to 26 down and 10 up to get A+ anything above that I get bad bufferbloat is this normal?

You can use the ifstatus command in OpenWrt to get information about your wan interface:

root@turris:~# ifstatus wan | grep device
	"l3_device": "pppoe-wan",
	"device": "eth2.7",

IN this example you could instantiate SQM on either pppoe-wan or eth2.7, personally I prefer pppoe-wan because then OpenWrt's hotplug will nicely tear down and re-instantiate the traffic shaper when my ISP re-news the PPPoE link (which results in the PPPoE being terminated and coming back up with a different IP address). But technically eth2.7 would work just as well.

It depends... an edgerouter X should allow traffic shaping to a combined up- down shaper rate of say 150Mbps, so your 100 should be within its capabilities (if you do not run too much other CPU-intensive stuff on the router). Now, bufferbloat above 26/10 could indicate either
a) that your router is massively overtaxed... in which case you could try to switch from piece_of_cake.qos/cake to simplest.qos/fq_codel for testing purposes. Cake will unfortunately allow more bufferbloat if it runs out of CPU cycles, while simplest.qos will simply not reach the configured shaper rate but will keep the latency under load increase relatively low.
b) your ISP is oversubscribing its infrastructure (which is an economic given all ISP need to oversubscribe, otherwise internet access would be either super slow or super expensive) and its bet against the users aggregated usage is failing...
c) or something completely different :wink:

Thanks for that info mate, Now iv'e noticed I cant get my speed above 35 mbps when SQM is active? I've tried all the SQM settings with no luck :confused: What could be causing it? I only use the router for SQM nothing else as well.EDIT

I've now turned off SQM and ran a speed test and its not giving me my full speeds the highest its going is 40mb and 18 up, thats why the SQM isn't working, is there a fix for this

EDIT now fully resolved, I add turn on offloading etc and now working fine with SQM even tho it says its not fully compatible :slight_smile: