SQM configuration /etc/config/sqm

The sqm-scripts package in OpenWrt controls Bufferbloat - the undesirable latency that comes from the router buffering too much data. Smart Queue Management (SQM) is our name for an intelligent combination of better packet scheduling (flow queueing) techniques along with with active queue length management (AQM).

The Smart Queue Management (SQM) - Minimizing Bufferbloat page tells how to configure SQM quickly.

This page discusses the values found in the SQM configuration file in /etc/config/sqm.

The queue section declares buffer parameters for an interface.

Name	Type	Required	Default	Description
`enabled`	boolean		no	enable or disable the queue section
`interface`	string	yes	eth0	interface name
`upload`	integer		2032	Upload speed (kbit/s) (egress) set to 0 to selectively disable egress shaping
`download`	integer		14698	Download speed (kbit/s) (ingress) set to 0 to selectively disable ingress shaping
`linklayer`	string		none	“none”, “ethernet”, or “atm”. Link-layer adaptation. See sqmlink_layer_adaptation_tab
`overhead`	integer		0	Per Packet Overhead, bytes
`tcMTU`	integer		2047	Maximal Size for size and rate calculations, bytes; needs to be >= interface MTU + overhead
`tcTSIZE`	integer		512	Number of entries in size/rate tables, TSIZE; for ATM choose TSIZE = (tcMTU + 1) / 16
`tcMPU`	integer		0	Minimal packet size, MPU (byte); needs to be > 0 for ethernet size tables
`ilimit`	integer		(none)	Hard limit on ingress queues; leave empty for default
`elimit`	integer		(none)	Hard limit on egress queues; leave empty for default
`itarget`	string		(none)	Latency target for ingress, e.g 5ms [units: s, ms, or us]; leave empty for automatic selection, put in the word default for the qdisc's default.
`etarget`	string		(none)	Latency target for egress, e.g. 5ms [units: s, ms, or us]; leave empty for automatic selection, put in the word default for the qdisc's default.
`ingress_ecn`	string		ECN	“ECN” or “NOECN”. Explicit congestion notification (ECN) status on inbound packets (ingress)
`egress_ecn`	string		ECN	“ECN” or “NOECN”. Explicit congestion notification (ECN) status on outbound packets (egress)
`target`	string		5ms	Latency target for ingress, e.g 5ms [units: s, ms, or us]; leave empty for automatic selection, put in the word default for the qdisc's default.
`squash_dscp`	integer		1	Squash DSCP on inbound packets (ingress). 1 = squash, 0 = do not squash
`squash_ingress`	integer		1	Ignore DSCP on ingress. 1 = ignore, 0 = allow
`qdisc`	string		fq_codel	fq_codel efq_codel nfq_codel sfq codel ns2_codel pie sfq cake (availability varies, check /var/run/sqm/available_qdiscs)
`script`	string		simple.qos	Queue setup script (see table below)
`iqdisc_opts`	string		(none)	Advanced option string to pass to the ingress queueing disciplines; no error checking, use very carefully.
`eqdisc_opts`	string		(none)	Advanced option string to pass to the egress queueing disciplines; no error checking, use very carefully.
`qdisc_advanced`	boolean		false	[only used by the luci-app-sqm package]
`qdisc_really_really_advanced`	boolean		false	[only used by the luci-app-sqm package]

Name	Default	Description
`simple.qos`	yes	BW-limited three-tier prioritisation scheme with fq_codel on each queue.
`simplest.qos`	no	Simplest possible configuration: HTB rate limiter with your qdisc attached.
`layer_cake.qos`	no	This uses the cake qdisc as a replacement for htb as shaper and fq_codel as leaf qdisc. This exercises cake's diffserv profile(s) as different “layers” of priority. This script requires that cake is selected as qdisc. See: http://www.bufferbloat.net/projects/codel/wiki/Cake for more information
`nxt_routed_hfsc.qos`	no	Uses a combination of HFSC and FLOW classifier to prioritize typical interactive protocols. This script is specially designed for clients behind NAT.
`piece_of_cake.qos`	no	This just uses the cake qdisc as a replacement for htb as shaper and fq_codel as leaf qdisc. It just does not come any simpler than this, in other words it truly is a “piece of cake”. This script requires that cake is selected as qdisc. See: http://www.bufferbloat.net/projects/codel/wiki/Cake for more information

Only Available in DD Trunk

[ The following refers to the 2017 OpenWrt DD effort that has been superseded by the LEDE-based release. The DD version never was released, so this information needs to be updated/removed. ]

The following scripts have been added after the release of CC 15.05.1, and will presumably be in DD:

Name	Default	Description
`simplest_tbf.qos`	no	Simplest possible configuration (TBF): TBF rate limiter with your qdisc attached. TBF may give better performance than HTB on some architectures.
`hfsc_lite.qos`	no	This three band HFSC configuration is intended for a common residential router. It uses extremely simplistic protocol/port filtering for bands and prioritises bandwidth over low delay in case of insufficient CPU power.
`hfsc_litest.qos`	no	This single band HFSC configuration is the bare minimum. Prioritises bandwidth over low delay in case of insufficient CPU power. The lack of filter before the QDISC may help reduce CPU load.

SQM configuration /etc/config/sqm

Sections

Queue Setup Scripts

Only Available in DD Trunk