This repository contains a historical archive of the DualPI2 code.
See https://github.com/L4STeam for newer work.
sch_dualpi2: DualPI2 AQM module for Linux
PI2 AQM is both an extension, and a simplification of the PIE (PI-Enhanced AQM). It makes quite some heuristics unnecessary, while enabling it to control scalable (L4S = low loss, low latency and scalable) congestion controls (like DCTCP, TCP-Prague, ...). Both Reno/Cubic can be used in parallel with DCTCP, giving it the same throughput.
The DualQ option can be used to classify the L4S traffic in a priority low latency queue, enabling L4S's full low latency power. The drop/mark coupling makes sure that the flows are still fair (now only congestion window fair as, due to the different Q sizes, their RTT will be different).
DualPI2 AQM is an improved and extended version of PI2 AQM.
Main differences:
- dualq by default
- 2 configurable overload strategies:
- limits the drop probability to align with maximum L4S marking
- or switches to drop for l4s queue if drop probability exceeds configured threshhold
- uses sojourn time to estimate queue delay
- classic drop at either enqueue or dequeue (default), depending on what is configured
- accepts actual values of alpha and beta parameters as floats (they had to be multiplied by 16 in PIE and PI2)
PI2 and DUALPI2 AQMs are implemented as modules. In order to use any of those, you need to either reinstall iproute2 package or use a local build of tc from iproute2. The files that should be added/changed and a patch are included in this repository. Currently only tested with iproute2 version 3.16.0.
Build iproute2 locally:
- download iproute2 package from https://www.kernel.org/pub/linux/utils/net/iproute2/
- apply patch or copy over the files manually
cd iproute2-l4s && make
Reinstall iproute2:
cd iproute2-l4s && make install
Build sch_ module:
cd sch_<aqm> && make
Register module:
cd sch_<aqm> && make load
Remove module:
cd sch_<aqm> && make unload
Add as a qdisc with a bottleneck of 40Mbps:
sudo tc qdisc del dev <interface> root
sudo tc qdisc add dev <interface> root handle 1: htb default 10
sudo tc class add dev <interface> parent 1: classid 1:10 htb rate 40Mbit ceil 40Mbit burst 1516
sudo tc qdisc add dev <interface> parent 1:10 <aqm>
or with parameters:
sudo tc qdisc add dev <interface> parent 1:10 dualpi2 <parameters>
-
Dependencies:
bison libdb-dev flex
All time parameters are in TC-defined time units and can be followed by an optional unit [s|ms|us] or used as bare numbers in microseconds (Example: 20ms or 20000).
limit [packets] : number of packets that can be enqueued
target [time] : user specified target delay in pschedtime
tupdate [time] : timer frequency
alpha : integral gain factor, used to scale the change in queuing time
beta : proportional gain factor, used to scale the change in queuing time comparing to previous measurement
no_dualq | l4s_dualq | dc_dualq :
no_dualq: single queuel4s_dualq: dual queue for ECT(1) and CEdc_dualq: dual queue for ECT(0), ECT(1) and CE (DCTCP compatibility)
k : coupling rate factor between Classic and L4S
no_ecn | classic_ecn | l4s_ecn | dc_ecn :
no_ecn: no scalable markingclassic_ecn: ecn (marking) supportl4s_ecn: scalable marking for ECT(1) onlydc_ecn: scalable marking for ECT(0) and ECT(1) (DCTCP compatibility)
l_thresh [time] : sojourn queue size when LL packets get marked
t_shift [time] : L4S FIFO time shift
c_limit | l_drop :
c_limit: limit Classic taildrop to 100% probability divided by k, sets l_drop to 0: no drop applied at all to ECT packetsl_drop[PROBABILITY between 0 and 100] : L4S max probability where classic drop is applied to all traffic
drop_enqueue | drop_dequeue
drop_enqueue: drop on enqueuedrop_dequeue: drop on dequeue
limit : 1000
target : 20ms
tupdate : 30ms
alpha : 0.3125
beta : 3.125
l4s_dualq
k : 2
l4s_ecn
l_thresh : 1ms
t_shift : 40ms
c_limit
drop_dequeue
- Repo owner or admins olga@albisser.org or koen.de_schepper@nokia-bell-labs.com
- Other community or team contact