Cache Prefetch Hint Mechanism for Reducing Redundant Requests
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Solution Overview
Problem
Conventional cache prefetching systems in processor-based systems often result in duplicated effort and resource wastage due to unawareness of outstanding prefetch requests between L1 and L2 caches, leading to unnecessary power consumption and latency.
Innovation Solution
Implementing a prefetch hint mechanism where the number of outstanding prefetch requests is stored and forwarded between caches, allowing the higher-level cache to skip already requested addresses and optimize its prefetch stream based on this information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cache prefetching systems independently issue requests without awareness of other caches' outstanding requests, then each cache can maintain its own prefetching strategy, but redundant prefetch requests are generated causing power consumption and latency increases
Solution Approach 1:
The patent implements a feedback mechanism where prefetch hint information about outstanding requests is communicated from lower-level caches (L1) to higher-level caches (L2). This feedback allows the L2 cache to awareness of L1's prefetch activities and adjust its own prefetching behavior accordingly, eliminating redundant requests and reducing power consumption.
Solution Approach 2:
The patent introduces prefetch hint information as an intermediary mechanism that mediates between L1 and L2 prefetchers. This hint information acts as a communication channel that allows the L2 prefetcher to coordinate with L1 prefetching activities, preventing duplicate requests while maintaining independent prefetching strategies at each cache level.
2Productivity
If conventional cache prefetching systems independently issue requests without awareness of other caches' outstanding requests, then each cache can maintain its own prefetching strategy, but duplicated prefetch effort is generated causing resource wastage
Solution Approach 1:
The feedback mechanism transmits prefetch hint information from L1 to L2 caches, enabling the L2 prefetcher to recognize and skip addresses that are already being prefetched by L1. This reduces duplicated prefetch effort and optimizes resource utilization across the cache hierarchy.
Solution Approach 2:
The L2 prefetcher uses prefetch hints to perform partial prefetching by skipping addresses that are already covered by L1's outstanding requests. Instead of issuing complete independent prefetch sequences, the L2 prefetcher adjusts its action to only prefetch addresses not already requested by L1, reducing wasted resources.
3Ease of operation
If the L2 prefetcher issues requests without knowing about L1's outstanding prefetch requests, then the L2 cache can independently optimize its prefetch stream, but redundant requests increase latency
Solution Approach 1:
The prefetch hint feedback mechanism allows the L2 prefetcher to maintain independent optimization capabilities while avoiding redundant requests. By receiving information about L1's outstanding requests, the L2 prefetcher can adjust its prefetch stream to skip already-requested addresses, thereby reducing latency without sacrificing independent optimization.
4Device complexity
If prefetch requests are issued without coordination between cache levels, then simple independent prefetching logic can be used, but redundant requests consume unnecessary power and increase latency
Solution Approach 1:
The patent introduces prefetch hint information as a lightweight intermediary that enables coordination between L1 and L2 prefetchers without significantly complicating their logic. The hint mechanism provides just enough information for the L2 prefetcher to avoid redundant requests while maintaining relatively simple independent prefetching logic at each cache level.
Data Source
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AI summary
The present disclosure provides a method and apparatus for using prefetch hints. One embodiment of the method includes bypassing, at a first prefetcher (150) associated with a first cache (120), issuing requests to prefetch data from a number of memory addresses in a sequence of memory addresses determined by the first prefetcher. The number is indicated in a request received from a second prefetcher (!40) associated with a second cache (125). This embodiment of the method also includes issuing, from the first prefetcher, a request to prefetch data from a memory address subsequent to the bypassed memory addresses.