Killi: Runtime Fault Classification to Deploy Low Voltage Caches without MBIST
Bibliographic record
Abstract
Supply voltage (VDD) scaling is one of the most effective mechanisms to reduce energy consumption in high-performance microprocessors. However, VDD scaling is challenging for SRAM-based on-chip memories such as caches due to persistent failures at low voltage (LV). Previously designed LV-enabling mechanisms require additional Memory Built-in Self-Test (MBIST) steps, employed either offline or online to identify persistent failures for every LV operating mode. However, these additional MBIST steps are time consuming, resulting in extended boot time or delayed power state transitions. Furthermore, most prior techniques combine MBIST-based solutions with customized Error Correction Codes (ECC), which suffer from non-trivial area or performance overheads. In this paper, we highlight the practical challenges for deploying LV techniques and propose a new low-cost error protection scheme, called Killi, which leverages conventional ECC and parity to enable LV operation. Foremost, the failing lines are discovered dynamically at runtime using both parity and ECC, negating the need for extra MBIST testing. Killi then provides on demand error protection by decoupling cheap error detection from expensive error correction. Killi provides error detection capability to all lines using parity but employs Single Error Correction, Double Error Detection (SECDED) ECC for a subset of the lines with a single LV fault. All lines with more than one fault are disabled. We evaluate this completely hardware enclosed solution on a GPU write-through L2 cache and show that the Vmin (minimum reliable VDD) can be reduced to 62.5% of nominal VDD when operating at 1GHz with only a maximum of 0.8% performance degradation. As a result, an 8CU GPU with Killi can reduce the power consumption of the L2 cache by 59.3% compared to the baseline L2 cache running at nominal VDD. In addition, Killi reduces the error protection area overhead by 50% compared to SECDED ECC.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".