Timing-Aware Stream Prefetching for Microprocessor Cache
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Solution Overview
Problem
Existing data prefetching techniques lack consideration for timing, leading to untimely prefetches that cause cache pollution and bandwidth waste, limiting their effectiveness in bridging the processor-memory performance gap.
Innovation Solution
A stream timing technique that records and utilizes timing information between cache misses to adjust prefetch timing, incorporating a timing-aware stride prefetcher that chains local streams by time to generate timely prefetch candidates, reducing untimely prefetches and improving prefetch accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data prefetching is performed without timing consideration, then prefetch coverage is improved, but cache pollution and bandwidth waste increase due to untimely prefetches
Solution Approach 1:
The patent applies preliminary action by performing prefetching operations in advance based on predicted timing. The system calculates expected access times for future memory requests and issues prefetch commands before the actual access occurs, ensuring data arrives in the cache exactly when needed. This resolves the contradiction by maintaining high prefetch coverage while avoiding cache pollution through precise timing control.
Solution Approach 2:
The patent implements dynamics by making the prefetch timing adaptive and dynamic. The system continuously monitors actual access patterns and adjusts prefetch timing predictions dynamically, rather than using fixed intervals. This allows the prefetcher to adapt to changing workload characteristics and maintain optimal timing, preventing both early prefetches (cache pollution) and late prefetches (missed opportunities).
2Quantity of substance
If data prefetching is performed without timing consideration, then prefetch coverage is improved, but bandwidth waste increases due to untimely prefetches
Solution Approach 1:
The system performs preliminary action by calculating predicted access times for future memory requests and issuing prefetch commands in advance. By determining the optimal prefetch time based on historical access patterns and memory latency, the system ensures data is fetched through the memory hierarchy exactly when needed, maximizing prefetch coverage while avoiding bandwidth waste from premature or redundant transfers.
Solution Approach 2:
The patent implements feedback by monitoring actual memory access patterns and using this information to refine prefetch timing predictions. The system compares predicted access times with actual access times, adjusts its timing models accordingly, and uses this feedback to improve future prefetch decisions. This closed-loop approach ensures high prefetch coverage while minimizing bandwidth waste through increasingly accurate timing predictions.
3Measurement precision
If existing stream localization techniques are used, then prefetch accuracy is improved, but timing information is lost leading to untimely prefetches
Solution Approach 1:
The patent applies merging by combining stream localization techniques with timing information tracking. The system maintains localized streams based on address patterns while simultaneously recording timing data for each stream. This integration allows the prefetcher to identify not only what data to prefetch (through stream localization) but also when to prefetch it (through timing information), resolving the contradiction between prefetch accuracy and timing awareness.
Solution Approach 2:
The patent implements another dimension by adding the time dimension to the traditional stream localization approach. While conventional methods localize streams in address space, this system extends localization to include temporal characteristics, creating a two-dimensional view (address + time). This additional temporal dimension enables the system to maintain high prefetch accuracy through stream localization while simultaneously preserving and utilizing timing information for optimal prefetch scheduling.
4Ease of operation
If prefetch timing is not controlled, then prefetch simplicity is maintained, but performance is degraded due to late or early prefetches
Solution Approach 1:
The patent implements self-service by enabling the prefetcher to automatically determine and adjust its own timing without complex external control. The system uses its own historical access data to build timing models and make autonomous prefetch decisions. This self-service approach maintains operational simplicity while improving performance, as the prefetcher adapts to workload characteristics automatically without requiring complex scheduling algorithms or external intervention.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting prefetch timing parameters based on observed access patterns. The system monitors actual access intervals and uses this information to modify prefetch timing parameters, transforming the prefetch behavior to match actual workload characteristics. This adaptive parameter adjustment maintains simplicity by using straightforward timing models while significantly improving performance through optimized prefetch timing.
Data Source
AI summary
A method and apparatus for prefetching data from memory for a multicore data processor. A prefetcher issues a plurality of requests to prefetch data from a memory device to a memory cache. Consecutive cache misses are recorded in response to at least two of the plurality of requests. A time between the cache misses is determined and a timing of a further request to prefetch data from the memory device to the memory cache is altered as a function of the determined time between the two cache misses.