VirtualTimeKernel

This repository is based on the VT-Mininet, which aims to improve the performance fidelity and scalability of Mininet.

Motivation

Virtual time technique are mainly used for two applications in emulation/simulation:

1. Dilate emulation time so that more resources are available in emulation, e.g. link bandwidth.

2. Synchronize simulation and emulation, if they somehow need to work together, by freezing/unfreezing emulation freely.

In this project, we implement virtual time in the Linux kernel. Mininet can use the exported virtual time features through /proc virtual file system so that clocks inside emulated hosts/containers could be dilated/frozen/unfrozen.

Installation

Install Virtual Time Patch to Linux Kernel

• First, run ./install.sh both at the root directory of this repo, which will automatically:

  • Download and unpack Linux kernel version 3.16.3
  • Copy source files to the unpacked kernel
  • Build new kernel

• Configure GRUB so that you can select which kernel to boot

sudo vim /etc/default/grub
# edit following lines
GRUB_HIDDEN_TIMEOUT=15
GRUB_HIDDEN_TIMEOUT_QUIET=false
# exit editing
update-grub

• Reboot and select the newly built kernel image in grub menu.

Install Virtual Time Userspace Utilities

Install a couple virtual time userspace commands:

cd vt_userspace
make
sudo make install
cd ../

Install VT-Mininet

You can install by rebuild Mininet:

cd mininet # enter the mininet dir inside this repo
sudo make clean
sudo make install
cd ../

I will make a pull request to Mininet repo after more tests.

What's New (Comparing to VT-Mininet)

• We implement a different interface via /proc virtual file system. Two entries are added to each process: dilation and freeze.

  • Now dilating a process/container will be as simple as:

  echo $TDF > /proc/$PID/dilation
  

  • Freezing a process/container can be done using:

  echo 1 > /proc/$PID/freeze # freeze/pause
  echo 0 > /proc/$PID/freeze # unfreeze/resume
  

• In mnexec.c, starting a container will call unshare with an extra flag CLONE_NEWTIME.

• With the /proc interface, we can parallelize the operation of dilating/freeze a number of hosts in Mininet. Two utility programs, dilate_all_proc and freeze_all_proc, use pthread library to do "echoing" with multi-threads.

• In net.py I added two new method: dilateEmulation(self, tdf) and freezeEmulation(self, op='freeze'). Mininet users can use them to dilate/freeze emulation.

Experiments with Virtual Time

Under test_vtmininet there are two experiments using iperf3:

• vtmn_fidelity_tcp.py will run a network with string topology and test TCP throughput between 2 hosts.
• vtmn_fidelity_udp.py will run a network with string topology and test UDP throughput between 2 hosts.
• vtmn_freeze_iperf.py runs similar string-topo network and freeze emulation periodically.

More tests are on the way:

• vtmn_freeze_ping.py
• vtmn_scalability.py

Known Issues

• Dilated host will accidentally exit clock namespace after iperf3 exits.
• iperf2 is not tested yet.

Acknowledge

My implementation of virtual time is inspired by TimeKeeper wrote by Jeremy Lamps. Great thanks for sharing his source code and providing a very detailed documentation.