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Report — Multicore-OoO-sim

Phase-by-phase write-up of Multicore-OoO-sim from inception through the end of Phase 3 (April 2026). Written for a reader who knows computer architecture but hasn't necessarily worked with the C++ ecosystem (CMake, Catch2, CLI11, nlohmann/json) or with the trace-driven simulator world (ChampSim, DynamoRIO, Pin).

Reading order

If you're new to the project, start here:

  1. 00-overview.md — what this project is, the architecture diagram, the phased roadmap, the runnable status.
  2. 05-tools-and-libraries.md — one-page-per-tool tour of every external piece the codebase depends on. Read this before the phase docs if any of "CMake", "ChampSim", "DynamoRIO" feels unfamiliar.

Then the phase reports, in order:

  1. 01-phase0-skeleton.md — Phase 0: skeleton, build system, JSON config, CLI, logging, CI. No simulator behavior yet, but the foundation everything else lands on.
  2. 02-phase1-traces.md — Phase 1: trace format decision (ChampSim binary), reader/writer, synthetic generator, tracer plan. Includes a deeper explainer of why traces matter, what dynamic binary instrumentation is, and the public academic trace corpora.
  3. 03-phase2-cache.md — Phase 2: cache subsystem (--mode cache). Geometry, replacement policies (LRU, LIP, MIP), write policies (WBWA, WTWNA), prefetchers (+1, Markov, Hybrid). Pinned bit-for-bit against project1 reference output.
  4. 04-phase3-predictor.md — Phase 3: branch predictors (--mode predictor). Always-Taken, Yeh-Patt two-level adaptive, Perceptron, Hybrid tournament. Pinned bit-for-bit against project2's proj2sim binary.

And the standalone reviews:

  1. code-review.md — senior-level code review over Phases 0-3. Bugs (none found that affect output), logic / model-fidelity issues (some), and Phase 4 architectural debts (two important ones).
  2. 06-phase4-review.md — second review pass covering Phase 4A (cache MSHR) and Phase 4B (OoO core). Four bug-class findings that all live in the seam between subsystems — hybrid predictor under multi-branch-in-flight, Cache::issue() side-effect leak on MSHR-full, OoO LSU busy-loop on the same stall, and --mode coherence silent exit. All fixed in the same pass with tests pinning each regression.
  3. 07-phase5a-coherence.md — Phase 5A: --mode coherence. Five protocols (MI / MSI / MESI / MOSI / MOESIF), RING network, directory, FICI per-core trace driver. Pinned bit-for-bit against project3's dirsim reference outputs for (MSI / MESI / MOSI / MOESIF) × (4 / 8 / 12 / 16 cores) — 16 / 16 combos.
  4. 08-phase5b-full.md — Phase 5B: default invocation runs the full multi-core OoO + coherence simulator. N OoO cores, each with private finite L1+L2, all connected through the Phase 5A ring + directory + agents. The simulator engine is feature-complete after this phase.
  5. 09-config-sweep.md — post-5B configuration sweep: ~30 configs across cores / protocols / cache geometry / DRAM latency / OoO width / predictor. No deadlocks. Headline finding: aggregate IPC saturates at ~0.042 by 4 cores — the single ring + single directory + single DRAM channel is the bottleneck.

Status snapshot

Phase Subject Status Tests passing
0 Skeleton & infrastructure ✅ done n/a
1 Trace format & tracer partial 5
2 Cache (--mode cache) ✅ done 41 (incl. 4 proj1 regressions)
3 Branch predictor (--mode predictor) ✅ done 11 (incl. 1 proj2 regression with 4 sections)
4 OoO core (--mode ooo) ✅ done 8 (basic) + 4 from cache/predictor regressions covering Phase-4 fixes
5A Coherence (--mode coherence) ✅ done 20 (4 banner + 5 fici + 5 network/message + 3 MI synthetic + 4 proj3 regression cases × multi-core fan-out)
5B Multi-core OoO + coherence (default) ✅ done 18 (5 CLI dispatch + 4 coherence-sink + 5 WRITEBACK directory + 4 full-mode integration)
6 Polish & public release not started —

Total tests: 126 / 126 passing.

Build / run cheat sheet

# Configure + build
cmake --preset default
cmake --build --preset default

# Run cache mode
./build/default/sim --mode cache \
    --config configs/baseline.json \
    --trace tests/cache/fixtures/proj1/short_gcc.trace

# Run predictor mode
./build/default/sim --mode predictor \
    --config configs/baseline.json \
    --trace tests/predictor/fixtures/proj2/branchsim.champsimtrace

# Run all tests
ctest --preset default