Ditty: Directory-based Cache Coherence for Multicore Safety-critical Systems
Why this work is in the frame
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Bibliographic record
Abstract
Ditty is a predictable directory-based cache co-herence mechanism for multicore safety-critical systems that guarantees a worst-case latency (WCL) on data accesses. Prior approaches for predictable cache coherence use a shared snooping bus to interconnect cores. This restricts the number of cores in the multicore to typically four or eight due to scalability concerns. Ditty takes a first step towards a scalable cache coherence mechanism that is predictable and one that can support a larger number of cores. In designing Ditty, we propose a coherence protocol and micro-architecture additions to deliver a WCL bound that is lower than a naive approach. Our WCL analysis reveals that the resulting bounds are comparable to state-of-the-art bus-based predictable coherence approaches. We prototype Ditty in hardware and empirically evaluate it on an FPGA. Our evaluation shows the observed WCL is within computed WCL bound for both the synthetic and SPLASH-3 benchmarks. We release our implementation to the public domain.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it