gem5 Runahead

Implementation of Runahead Execution in the gem5 simulator

Features:

• A traditional runahead execution CPU model for gem5
• Short and overlapping period runahead elimination
• Runahead instruction stream filtering
• 4 runahead exit policies
  • Eager exit
  • Minimum work delayed exit
  • No load left behind delayed exit
  • Dynamic delayed exit

Setup

Clone the repository with

git clone --recurse-submodules https://github.com/halworsen/gem5-runahead.git

This will additionally clone v22.0.0.2 of gem5.

If you run Windows or just want to use a container, try the following. It's been a while since I used this myself, so things aren't guaranteed to be that smooth.

• Run make image to build a container image with all required and optional development packages + some utilities.
• Set the GEM5_DEV_DIR env variable to the path to this repository. Use make run to create/start a dev container with the GEM5_DEV_DIR mounted in the home directory.
• Navigate to the mounted directory and build gem5 with the runahead extensions using make gem5.
• Run gem5 with make run.

If you get CRLF-related errors, dos2unix can take care of that.

Building gem5 with the runahead extension

Runahead is implemented as a new CPU model which is based on the O3CPU model. The runahead CPU is structured as an extension of gem5 and can therefore be built by specifying EXTRAS when building gem5 with scons.

To build gem5 with the runahead extension, follow the gem5 documentation on building gem5 to setup any dependencies. Optionally setup a Python virtual environment with the Scons build tool

# create the virtual environment
python -m venv venv
# activate the virtual environment
source venv/bin/activate
# install scons
python -m pip install -r requirements.txt

Then build gem5 by running

make gem5

# specific build variants
make gem5-debug
make gem5-opt
make gem5-fast

# without runahead extensions
make gem5-bare