Fetch Directed Instruction Prefetching for gem5

This is the development repository for Fetch Directed Instruction Prefetching (FDP) in gem5 also known as decoupled front-end. FDP was originally published in MICRO'99. Today, FDP is the standard front-end design for high performance server CPU's including CPU's from Intel, IBM, AMD, and ARM.

This implementation is based on an industrial report and aims to establish a state-of-the-art front-end design comparable to modern servers in gem5.

How to use

We included an example script how to configure FDP correctly and simulate a simple "Hello World!" program. The script is tested with the x86, ARM, RISC-V ISA's which can be specified by the --isa flag.

```bash

Build gem5

scons build/ALL/gem5.opt

Run the simulation

./build/ALL/gem5.opt \ configs/example/gem5_library/fdp-hello.py \ --isa [--disable-fdp] ```

Notes

The implementation was developed for the X86 architecture in full-system mode. Other architectures were not extensively tested. If you encounter any issues, please let us know via issues, pull requests or PM to David Schall GitHub,web page. Furthermore, we welcome any feedback and ideas for improvements.

Reference our work

This work was done for our recent paper accepted to MICRO'23. If you use our work, please cite our paper: @inproceedings{10.1145/3613424.3614258, author = {Schall, David and Sandberg, Andreas and Grot, Boris}, title = {Warming Up a Cold Front-End with Ignite}, year = {2023}, publisher = {Association for Computing Machinery}, address = {Toronto, ON, Canada}, doi = {10.1145/3613424.3614258}, booktitle = {Proceedings of the 56th Annual IEEE/ACM International Symposium on Microarchitecture (MICRO '23)}, series = {MICRO'23} }

gem5 integration status

We are currently in the process of integrating the changes to the main gem5. It is a time-consuming process as the changes are extensive and require a lot of testing. This might cause conflicts if you try to merge the changes into the main gem5. We try to keep the list of the integration status up-to-date. Furthermore, it might be possible that some bugs are fixed while integrating the changes.

• [ ] cpu: Update BPU to support decoupled front-end
• [ ] cpu: Implement decoupled front-end
• [ ] cpu: Implement fetch target queue
• [ ] cpu: Implement taken-only history (#499)
• [ ] cpu: Implement fetch directed prefetcher
• [x] arch: Add instruction size and PC set methods (#357)
• [x] sim: Probe listener template with lambda (#356)
• [ ] cpu: Branch Predictor Refactoring (#455)
• [x] cpu: Refactor indirect predictor (#429)
• [x] cpu: Restructure RAS (#428)
• [x] cpu: Restructure BTB (#412)

The gem5 Simulator

This is the repository for the gem5 simulator. It contains the full source code for the simulator and all tests and regressions.

The gem5 simulator is a modular platform for computer-system architecture research, encompassing system-level architecture as well as processor microarchitecture. It is primarily used to evaluate new hardware designs, system software changes, and compile-time and run-time system optimizations.

The main website can be found at http://www.gem5.org.

Getting started

A good starting point is http://www.gem5.org/about, and for more information about building the simulator and getting started please see http://www.gem5.org/documentation and http://www.gem5.org/documentation/learning_gem5/introduction.

Building gem5

To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/documentation/general_docs/building for more details concerning the minimum versions of these tools.

Once you have all dependencies resolved, execute scons build/ALL/gem5.opt to build an optimized version of the gem5 binary (gem5.opt) containing all gem5 ISAs. If you only wish to compile gem5 to include a single ISA, you can replace ALL with the name of the ISA. Valid options include ARM, NULL, MIPS, POWER, SPARC, and X86 The complete list of options can be found in the build_opts directory.

See https://www.gem5.org/documentation/general_docs/building for more information on building gem5.

The Source Tree

The main source tree includes these subdirectories:

• build_opts: pre-made default configurations for gem5
• build_tools: tools used internally by gem5's build process.
• configs: example simulation configuration scripts
• ext: less-common external packages needed to build gem5
• include: include files for use in other programs
• site_scons: modular components of the build system
• src: source code of the gem5 simulator. The C++ source, Python wrappers, and Python standard library are found in this directory.
• system: source for some optional system software for simulated systems
• tests: regression tests
• util: useful utility programs and files

gem5 Resources

To run full-system simulations, you may need compiled system firmware, kernel binaries and one or more disk images, depending on gem5's configuration and what type of workload you're trying to run. Many of these resources can be obtained from https://resources.gem5.org.

More information on gem5 Resources can be found at https://www.gem5.org/documentation/general_docs/gem5_resources/.

Getting Help, Reporting bugs, and Requesting Features

We provide a variety of channels for users and developers to get help, report bugs, requests features, or engage in community discussions. Below are a few of the most common we recommend using.

• GitHub Discussions: A GitHub Discussions page. This can be used to start discussions or ask questions. Available at https://github.com/orgs/gem5/discussions.
• GitHub Issues: A GitHub Issues page for reporting bugs or requesting features. Available at https://github.com/gem5/gem5/issues.
• Jira Issue Tracker: A Jira Issue Tracker for reporting bugs or requesting features. Available at https://gem5.atlassian.net/.
• Slack: A Slack server with a variety of channels for the gem5 community to engage in a variety of discussions. Please visit https://www.gem5.org/join-slack to join.
• gem5-users@gem5.org: A mailing list for users of gem5 to ask questions or start discussions. To join the mailing list please visit https://www.gem5.org/mailing_lists.
• gem5-dev@gem5.org: A mailing list for developers of gem5 to ask questions or start discussions. To join the mailing list please visit https://www.gem5.org/mailing_lists.

Contributing to gem5

We hope you enjoy using gem5. When appropriate we advise charing your contributions to the project. https://www.gem5.org/contributing can help you get started. Additional information can be found in the CONTRIBUTING.md file.