ywkang
a796c1d2f7
Establish English as the canonical ADR language with Korean translations held in a parallel docs/adr-ko/ tree as derived artifacts (1:1 mirror). Promotion from adr-proposed/ to adr/ now writes English to adr/ and the Korean to adr-ko/; bidirectional sync rule documented in CLAUDE.md. - Migrate 30 ADRs in docs/adr/: 28 Korean-only translated to English, 2 bilingual pairs (ADR-0020, ADR-0023) consolidated (.en.md suffix dropped). ADR-0023 EN regenerated against KO source which had newer HW Realization Notes (D16-D23) section. - docs/adr-history/ left frozen by design (transitional state). - CLAUDE.md (Part 2): update ADR Lifecycle for 4-folder layout, mark docs/adr-ko/ as a Derived Artifact, add ADR Translation Discipline section covering bidirectional sync, conflict resolution (EN wins), and proposed-language freedom. - tools/verify_adr_lang_pairs.py: new verification tool checking pair completeness, filename mirroring, ADR-ID match, Status byte-equality. Pre-commit hook intentionally not added; run on demand or in CI. - tests/test_verify_adr_lang_pairs.py: 11 cases including CRLF/LF normalization, em-dash title separator, underscore-slug edge case. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
77 lines
3.2 KiB
Markdown
77 lines
3.2 KiB
Markdown
# ADR-0004: Memory Semantics & Local-HBM Bandwidth Guarantee
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## Status
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Accepted
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## Context
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Accurately modeling PE↔HBM behavior is essential for kernel latency estimation.
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Each PE has a notion of “local HBM” that must guarantee full HBM bandwidth, independent of intervening on-die fabric bandwidth.
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## Decision
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### D1. Local HBM definition
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- Each PE is assigned a logically defined “local HBM” region.
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- Local HBM corresponds to the pseudo-channel subset directly attached to that PE’s
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router in the NOC mesh (ADR-0017 D4).
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- The path is: PE_DMA → local router → HBM_CTRL (switching overhead only, 0 mesh hops).
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- The mapping (HBM pseudo-channels → PE local regions) is derived from topology configuration.
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### D2. Local HBM bandwidth guarantee contract
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- Accesses from a PE to its local HBM MUST guarantee full effective HBM
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read/write bandwidth independent of intervening fabric bandwidth limits.
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- Effective HBM bandwidth = spec bandwidth x efficiency factor.
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The efficiency factor (configured via `hbm_ctrl.attrs.efficiency`, default 0.8)
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models real-world DRAM inefficiencies (refresh cycles, bank conflicts, page
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misses). For example: 256 GB/s spec x 0.8 = 204.8 GB/s effective.
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- The topology builder applies the efficiency factor to router-to-hbm edge
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bandwidth at graph construction time, so all downstream routing and latency
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computation uses the effective value.
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- This guarantee is modeled by:
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- a dedicated logical path and/or service model that enforces HBM BW at the PE-local-HBM interaction point,
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- while still incurring non-zero latency along explicitly modeled components.
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- HBM CTRL internal modeling (PC striping, cut-through, scheduling fidelity)
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is consolidated in ADR-0033 (Latency Model: Assumptions and Known
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Simplifications). The aggregate BW guarantee here remains the contract;
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ADR-0033 documents how the per-PC model realizes it and which scheduler
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effects are intentionally simplified.
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### D3. Remote PE HBM semantics (intra-cube)
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- A PE that accesses another PE's local HBM traverses the NOC:
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- PE_DMA → NOC → (fabric hops) → target PE's NOC port → HBM_CTRL
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- NOC bandwidth and hop count may limit remote HBM access relative to local access.
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### D4. Non-local HBM semantics (inter-cube / inter-SIP)
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- Accesses from a PE to HBM in a different cube or SIP MAY be limited by:
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- NOC bandwidth within the cube,
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- inter-cube UCIe links,
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- inter-SIP fabric (PCIe/UAL).
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- These paths MUST be explicit and traceable.
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### D5. Shared SRAM semantics
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- Each CUBE contains a shared SRAM accessible by all PEs in that CUBE.
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- Access path: PE_DMA → NOC → shared SRAM.
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- Shared SRAM bandwidth is limited by the NOC↔SRAM link bandwidth.
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- Shared SRAM is not part of the HBM address space; it is a separate memory domain.
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## Verification Notes
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Tests should cover:
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- local-HBM case: BW matches HBM BW regardless of fabric BW parameter
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- remote PE HBM case: latency includes mesh hop traversal
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- non-local cases (inter-cube/inter-SIP): BW/latency respond to fabric/link parameters
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- shared SRAM case: access via NOC with correct BW
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## Links
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- SPEC R2/R5
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- ADR-0002 (distance/order & explicit bypass)
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- ADR-0017 D7 (PE DMA data paths through NOC to HBM)
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