Dynamic Prefetch Stream Priority Adjustment for Cache Miss Reduction
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Solution Overview
Problem
Conventional data prefetching systems in computer processors often lead to premature data return and cache line replacement, causing processor stalls due to equal prioritization of all prefetch streams, resulting in potential misses for higher-priority streams that require data sooner.
Innovation Solution
A method and system for dynamically adjusting prefetch stream priority based on the consumption rate of the processor, where the prefetch engine monitors the time between prefetch request completion and processor demand, and adjusts the priority to ensure higher-priority streams are prefetched more frequently, thereby optimizing data availability and reducing misses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If round-robin scheduling is used for prefetch streams, then all streams receive equal access, but higher-priority streams may suffer misses due to equal prioritization
Solution Approach 1:
The patent implements dynamic priority adjustment where the prefetch engine monitors the consumption rate of each prefetch stream and adjusts priorities in real-time. High-priority streams that consume data faster are assigned greater prefetch priority, while lower-consumption streams receive reduced priority. This dynamic mechanism resolves the contradiction by adapting to actual data consumption patterns rather than using static round-robin scheduling.
Solution Approach 2:
The system changes the priority parameter of prefetch streams based on monitored consumption rates. When a stream demonstrates high data consumption rate, its priority parameter is increased to ensure adequate prefetching resources. This parameter adjustment allows the system to differentiate between streams with different importance levels and prevent misses in critical streams.
2Loss of time
If early prefetching is performed to hide memory latency, then data operations can execute with minimal delay, but cache lines may be replaced before data is demanded by the processor
Solution Approach 1:
The patent employs dynamic priority adjustment to control prefetch timing and data retention. By monitoring consumption rates and adjusting priorities, the system ensures that prefetched data from high-priority streams is retained in the cache longer and given precedence during cache replacement decisions. This dynamic mechanism prevents premature eviction of needed data while still enabling early prefetching to hide latency.
Solution Approach 2:
The prefetch engine implements feedback by monitoring whether prefetched data is actually demanded by the processor. When data is demanded, the system learns from this feedback and adjusts future prefetch behavior. The monitoring of consumption rates provides continuous feedback that guides priority adjustments, ensuring that prefetching strategies adapt to actual usage patterns and prevent both premature return and premature replacement.
3Adaptability or versatility
If multiple prefetch streams are serviced concurrently, then all data streams are processed, but cache resources may be insufficient leading to misses in high-priority streams
Solution Approach 1:
The patent applies local quality by differentiating treatment among different prefetch streams based on their individual characteristics. Instead of uniform handling, each stream receives priority treatment proportional to its data consumption rate and importance. High-priority streams receive preferential cache allocation and prefetch resources, while lower-priority streams receive reduced resources. This localized differentiation resolves the contradiction by ensuring critical streams maintain high hit rates even in multi-stream environments.
Solution Approach 2:
The system dynamically changes priority parameters for different streams based on monitored consumption rates. This parameter adjustment allows the cache and prefetch engine to allocate resources unevenly according to actual needs, ensuring that high-priority streams receive sufficient resources to maintain high hit rates while still supporting multiple concurrent streams.
Data Source
AI summary
A method, processor, and data processing system for dynamically adjusting a prefetch stream priority based on the consumption rate of the data by the processor. The method includes a prefetch engine issuing a prefetch request of a first prefetch stream to fetch one or more data from the memory subsystem. The first prefetch stream has a first assigned priority that determines a relative order for scheduling prefetch requests of the first prefetch stream relative to other prefetch requests of other prefetch streams. Based on the receipt of a processor demand for the data before the data returns to the cache or return of the data along time before the receiving the processor demand, logic of the prefetch engine dynamically changes the first assigned priority to a second higher or lower priority, which priority is subsequently utilized to schedule and issue a next prefetch request of the first prefetch stream.