Self-Clocked Round Robin Packet Scheduling Paper Artifacts

Please check out our paper at https://www.usenix.org/conference/nsdi25/presentation/sharafzadeh. Citation key:

@INPROCEEDINGS{scrr,
  title={Self-Clocked Round-Robin Packet Scheduling},
  author={Sharafzadeh, Erfan and Matson, Raymond and Tourrilhes, Jean and Sharma, Puneet and Ghorbani, Soudeh},
    booktitle   = "NSDI",
    year        = "2025"
}

SCRR is a low-latency, zero-configuration, and fair packet scheduling paradigm that aims to replace existing fair packet schedulers such as Deficit Round-Robin (DRR).

This repository contains the qdisc implementation of SCRR and all the packets schedulers we tested in our paper, as well as tc modules and Linux kernel patches to replicate our test environment. The repository is forked from https://github.com/jean2/scrr which may contain a more up to date codebase for the schedulers. Check the paper for the explanation of the provided schduling modules.

Setting Up The Environment

Preparing the Kernel

1. Download and decompress Linux kernel 6.1
2. Apply the provided patches (*.diff). The patches include l4s functionality and support for TCP BBRv3.
3. Copy the qdisc modules (sch_*.c into kernel's net/sched/)
4. Add the sources to the corresponding Makefile in net/sched/Makefile:

obj-$(CONFIG_NET_SCH_SCRR)   += sch_scrr.o

5. Add the qdiscs to kernel's KConfig in net/sched/Kconfig:

 config NET_SCH_SCRR
      tristate "self-clocked round-robin packet scheduler"
      help
        Say Y here if you want to use the SCRR Scheduler.
        To compile this code as a module, choose M here: the module
        will be called sch_scrr.
 
        If unsure, say N.

Make sure to follow steps 4 and 5 for each qdisc module separately. 6. Compile and install the kernel:

make -j
make modules_install
sudo make install
reboot

7. If modules are not loaded, or you used make modules to only build kernel modules, use modprobe sch_scrr, or insmod sch_scrr.ko where appropriate to load the module.

Preparing iproute2

1. Download iproute2 sources for kernel 6.1
2. Unpack the archive and copy the tc modules (q_*.c) into tc/ directory.
3. Add the entries in tc/Makefile:

TCMODULES += q_scrr.o

4. Build iproute and install the excecutable in your path.

Loading the Scheduler

To load SCRR, use your custom built tc.

tc qdisc add dev NETDEVICE root scrr

Experiment Data

We have published the raw experiment data of SCRR paper at https://zenodo.org/records/14963380.

The data is in gzip format. After decompressing the archives, the following files are accessible:

*snd.icsv   -> iperf sender log
*rcv.icsv   -> iperf receiver log
*tcstats.txt    -> tc -s output
*.kperf     -> perf output (used to measure CPU utilization of modules)
*.pcap      -> packet capture data for some experiments

Method names can be decoded from file names. Files usually follow this format SENDER-IP_RECEIVER-IP_METHOD-ID_* Methods used in the paper correspond to the following IDs:

74  -> 'aifo'
83  -> 'drr+sfo-500'
84  -> 'drr+sfo-200'
86  -> 'drr+sfo_1500'
87  -> 'drr+sfo_9000'
92  -> 'scrr'
98  -> 'scrr-nmne'
99  -> 'scrr-npm'
101 -> 'stfq'
102 -> 'sp-pifo'
111 -> 'scrr-neia'
113 -> 'drr-200'
114 -> 'drr-500'
116 -> 'drr-1500'
117 -> 'drr-9000'
120 -> 'scrr-basic'

Please contact the authors for additional information about using the artifacts.

---

SCRR Authors March 2025