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@rappdw rappdw commented Nov 5, 2025

Summary

This PR updates the GPU implementation plans under .plans/gpu_implementation to address correctness and completeness issues identified in the initial draft. It corrects scaling assumptions, introduces formal semiring and masking abstractions, replaces the kernel sketch with a proper two-phase sparse matrix multiplication (SpGEMM) design, and adds unified memory (UVM) performance guidance.

Key Updates

  • Fixed scale arithmetic: Corrected the 1B×1B @ 0.1% density example (previously understated by ~10⁶×). The plan now frames scalability in terms of edges per node (O(n)) and provides realistic CSR memory budgets for billion-scale graphs.
  • Semiring and Mask abstractions: Introduces SemiringSpec and MaskSpec as first-class concepts to define the avos semiring and structural masks (e.g., upper-triangular).
  • Two-phase SpGEMM: Replaces the naïve nested-loop kernel with a standard symbolic → numeric design supporting deterministic (merge-based) and fast (hash-based) variants.
  • Deterministic mode: Adds a bit-exact path for validation, plus a fast path using atomics for production workloads.
  • Unified Memory guidance: Clarifies that UVM still requires cudaMemPrefetchAsync and cudaMemAdvise for performance on GH200/H100 systems.
  • Index width policy: Documents when to switch indptr to int64 for billion-scale workloads.
  • Testing and performance plans: Expands test coverage (property-based, adversarial, deterministic vs fast) and defines perf experiments including UVM on/off and cuSPARSE baselines.
  • Implementation phases: Refactors the roadmap to explicitly separate symbolic, numeric, and optimization phases.

Impact

No code changes yet—this PR revises the planning documents only. These updates make the GPU plan mathematically correct, technically credible, and aligned with state-of-the-art sparse GPU practice.

Next Steps

  • Implement deterministic symbolic/numeric kernels.
  • Add UVM prefetch/advice tuning hooks.
  • Integrate deterministic/fast mode toggling and performance CI.

- Created detailed planning documents for GPU acceleration
- Updated for DGX Spark (Grace Hopper) with unified memory
- Optimized for upper triangular matrices (50% savings)
- Target: 1B×1B matrices at 0.1% density on single H100
- Timeline: 8-12 weeks with two-tier approach

Key documents:
- 00_UPDATED_CONTEXT.md: Impact analysis of DGX/triangular/billion-scale
- IMPLEMENTATION_STRATEGY.md: Concrete implementation approach
- QUICK_START.md: Quick reference guide
- 01-06: Detailed architecture, kernels, API, testing, phases
- EXECUTIVE_SUMMARY.md: High-level recommendations

Changes from original plan:
- Unified memory simplifies architecture (30% less code)
- Triangular optimization for 50% performance gain
- Single-GPU first (Tier 1), multi-GPU later if needed (Tier 2)
- Same timeline but better outcome
…UVM tuning; deterministic mode; perf/tests updates
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github-actions bot commented Nov 5, 2025

Code Coverage

Package Line Rate Complexity Health
. 68% 0
core 92% 0
reference 98% 0
sparse 85% 0
sparse.csgraph 83% 0
types 100% 0
util 70% 0
Summary 83% (763 / 920) 0

Minimum allowed line rate is 65%

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github-actions bot commented Nov 5, 2025

Code Coverage

Package Line Rate Complexity Health
. 68% 0
core 92% 0
reference 98% 0
sparse 85% 0
sparse.csgraph 83% 0
types 100% 0
util 70% 0
Summary 83% (763 / 920) 0

Minimum allowed line rate is 65%

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rappdw commented Nov 5, 2025

From Sonnet 4.5 (Thinking)

Verdict

LGTM - Ready to Merge 🚀

This PR transforms the GPU implementation plan from a preliminary sketch into a production-ready technical specification. The math corrections alone justify the merge, and the formal abstractions (SemiringSpec, MaskSpec) will pay dividends during implementation and testing.

No blocking issues identified. The plan is technically sound, well-documented, and properly scoped.

@rappdw rappdw merged commit a763d9f into master Nov 5, 2025
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@rappdw rappdw deleted the feature/gpu-plan-update branch November 5, 2025 14:29
rappdw added a commit that referenced this pull request Nov 5, 2025
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2 participants