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PowerTCP kernel module

Important

The kernel module is missing a source of telemetry (the integration is prepared). Therefore, the powertcp congestion control in the module is only a proof of concept.

Note

The rttpowertcp in the kernel module is functional but—due to limitations in the kernel—lacks access to higher-precision hardware timestamps.

Following are step-by-step instructions on how to use and experiment with the PowerTCP kernel module. All commands listed here are assumed to be executed in the root folder of this repository.

When loaded into the kernel, the congestion control algorithms are called powertcp and rttpowertcp.

Prerequisites

  • Any recent Linux kernel and corresponding kernel headers
  • gcc
  • make
  • dkms (optional)

Preparation

The preparation steps need to be executed on both client and server.

  1. Install required packages (as root/with sudo):

    apt install gcc linux-headers-$(uname -r) make

    Ideally, tune the network interface IFACE for low latency etc. (as root/with sudo):

    apt install ethtool procps tuned
./tools/tune-eth IFACE

  2. Build the PowerTCP module implementation:

    make

On the server

Close any previously opened screen sessions that were opened this way.

Start iperf and iperf3 server instances, ready to use PowerTCP, in a screen session (as root/with sudo):

./tools/setup-module iperf-servers

Beware: You are root user inside the screen session!

Algorithm parameters (see On the client) do not need to be set on the server, they are irrelevant here.

On the client

The setup-module script opens a screen session readily prepared to use PowerTCP.

You can and should pass algorithm parameters to setup-module, e.g (as root/with sudo):

./tools/setup-module iperf-client host_bw=25000 hop_bw=25000 base_rtt=50

For a list of the available parameters see

/sbin/modinfo tcp_powertcp.ko

Note that a value for the gamma parameter must be multiplied with the value of power_scale defined in powertcp_defs.h and rounded to an integer afterwards.

Beware: You are root user inside the screen session!

Inside the screen session, you can, e.g,

  • run iperf3 (or iperf, the options differ) 
    iperf3 -N -C rttpowertcp -c SERVER_IP

Installation through DKMS

The kernel module is prepared for system-wide installation through DKMS. The Makefile provides a convenience target for installation through DKMS (as root/with sudo):

make dkms_install

Tracepoints

There are tracepoints to follow the algorithm, mainly for the three core functions defined in the paper and the values used and returned by them. The tracepoints can be found in /sys/kernel/debug/tracing/events/powertcp.

They can be enabled for example (see Event Tracing) with (as root/with sudo)

echo 1 > /sys/kernel/debug/tracing/events/powertcp/enable

and shown with (as root/with sudo)

cat /sys/kernel/debug/tracing/trace_pipe

or used with any other of the available tools, like bpftrace.

Development Resources