Monthly gem5 Developers' Meeting - March12th at 4pm (UTC)

[Harshil2107]

The monthly gem5 Developers' Meeting will take place on March 12th at 4pm UTC.

If you would like to add anything to the agenda please create a comment below.

Agenda:

• Alternative gem5 build build: replace SCons with CMake+Ninja and Bazel build systems #2969

Meeting information:

Microsoft Teams meeting

Join:
https://teams.microsoft.com/meet/2430032964825?p=SoQfMn8mejCKR8ahaf

Meeting ID:
243 003 296 482 5

Passcode:
Gp2tZ7tb

[powerjg]

Link to my slides: https://docs.google.com/presentation/d/1koWlqauvIPrmZ0HR6nkH2TU5wKh5nmXOQ0eHk3qlT38/edit?usp=sharing

[BobbyRBruce]

Meeting recording

A recording of the meeting can be found at https://youtu.be/WtYTw7WOrOo

Slides

gem5-monthly-developers-meeting-20260312.pptx
gem5-monthly-developers-meeting-20260312.pdf

gem5+bazel status March 2026.pptx
gem5+bazel status March 2026.pdf

Meeting notes

These meeting notes are AI generated

Agenda & Discussion Summary

1. gem5 Workshop @ ISCA 2026 (June 27, Raleigh, NC)

   • Workshop accepted as a full-day, in-person Saturday event (approx. 8:30–16:00).
   • Format: invited keynote (TBA), panel/town hall, and community presentations (target 20 min + 5 min Q&A per talk).
   • CFP highlights:
     • Submission deadline: April 24, 2026 (AoE)
     • 1-page double-blind PDF describing title, motivation, key insights, status, and planned content.
     • Review criterion: “Would this interest the gem5 community?”
     • Submission portal: HotCRP, linked from the event page.
     • Attendance requires in-person presenter (no remote presentations).
   • Bobby will keep the event page updated (https://www.gem5.org/events/isca-2026).
   • Jason is forming the Program Committee; volunteers (esp. students seeking review experience) are welcome—contact him directly.
   • Expect additional email reminders/announcements via SIGARCH, TCCA, and GitHub Discussions.

2. Build System Migration Discussion (SCONS → CMake/Bazel)

   • Sihao (UCLA) presented PR build: replace SCons with CMake+Ninja and Bazel build systems #2969: replaces SCons with CMake and adds an overlay Bazel build, citing:
     • 14 hours of iterative AI-assisted development (Claude & Codex) plus ~2 days total compute (≈$500 tokens).
     • Binary-identical outputs to SCons builds on his workstation; majority of CI checks pass.
     • Failures seen were mostly disk-space issues on CI runners; GPU tests skipped due to Docker constraints.
     • Current limitations: GPU/systemC optional flags not exhaustively validated; needs broader community testing.
     • Bazel implementation mirrors LLVM’s overlay approach (build files live in a dedicated directory).
     • Offers to share methodology/prompts via the Humanize workflow tool he created.
   • Discussion points:
     • Matt: Concerned about the migration burden of switching build systems; opposed to maintaining multiple systems long-term; wants clarity on overlay vs. native Bazel approach.
     • Sandeep: Wants phased migration (keep SCons as production, test new system as “experimental” before cut-over); asks why Bazel is beneficial (distributed builds, caching).
     • Giacomo: Favors a phased approach (possibly mirror LLVM: core build system + Bazel overlay) to allow orgs to transition at their own pace; stresses avoiding more than two systems simultaneously.
     • Jason: Emphasized a strategic decision first: what problems are we trying to solve?
       • SCons is hard to maintain/onboard.
       • Jason’s personal goal: treat gem5 as a standard Python library (no embedded interpreter), enabling distribution (e.g., pip/apt) and selective dynamic linking of only needed components.
       • His Bazel prototype builds each component into separate .so files, linking only what a simulation requires (contrast to CMake approach that still produces one large binary).
       • No strong preference from him yet—encourages community input.
   • Consensus / Next Steps:
     • Avoid merging PR build: replace SCons with CMake+Ninja and Bazel build systems #2969 as-is until community agrees on direction (CMake only? Bazel only? Both?).
     • Recognize maintaining SCons + CMake + Bazel simultaneously is untenable; eventual plan should delete SCons in the same change that introduces the replacement.
     • Need a dedicated GitHub Discussion thread to weigh pros/cons, desired workflow, migration strategy, and required features (GPU, SystemC, Kconfig, packaging).

3. Other Notes

   • Time ran out (~1 hour) before open mic; plan to continue build system discussion asynchronously.
   • No additional agenda items raised by others during the recording.

Useful Links

• Workshop info & CFP: https://www.gem5.org/events/isca-2026
• Workshop submission (HotCRP): https://gem5workshop2026.hotcrp.com
• Discussion thread for this meeting: https://github.com/orgs/gem5/discussions/2985
• Build system PR (for review/comments): build: replace SCons with CMake+Ninja and Bazel build systems #2969