Processor Cache Redirection to Reduce Conflict Misses
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Solution Overview
Problem
Existing processor caches suffer from inefficiencies due to conflict misses and thrashing, leading to reduced cache utilization and increased latency, particularly in scenarios where cache lines are full and memory blocks need to be evicted, resulting in frequent cache misses.
Innovation Solution
Implementing a redirection mechanism in processor caches that allows memory blocks to be redirected from a full cache line in a default set to an empty cache line in a different set, with metadata management to track these redirections, thereby improving cache utilization and reducing conflict misses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a memory block is stored in a full cache line of a default set, then cache utilization is maximized, but conflict misses increase and retrieval performance degrades
Solution Approach 1:
The patent introduces a redirection dimension by adding a redirection field to cache line metadata. When a memory block cannot be stored in its default set due to full cache lines, the system redirects it to an alternate set, effectively adding a new dimension (alternate set index) to the cache storage space. This resolves the contradiction by providing an additional storage pathway that maintains high cache utilization while preventing conflict misses from degrading retrieval performance.
2Productivity
If metadata is maintained to track redirections, then cache efficiency improves, but device complexity increases
Solution Approach 1:
The patent segments the cache metadata into distinct functional components: valid bit, dirty bit, tag, and redirection field. Each segment serves a specific purpose, allowing the system to track redirections efficiently without overwhelming complexity. The redirection field is further segmented into set index and tag portions, enabling precise identification of alternate storage locations. This segmentation improves cache efficiency while keeping metadata management tractable through modular organization.
3Reliability
If memory blocks are redirected to alternate sets, then conflict misses are reduced, but access latency increases
Solution Approach 1:
The patent performs preliminary action by checking the redirection field during the cache access process. When a memory block is accessed, the system first checks the default set, then immediately checks the redirection field to determine if the block was redirected to an alternate set. This preliminary check mechanism ensures that redirection overhead is minimal, as the redirection information is already prepared and stored in the metadata, allowing fast access without significant latency penalty while effectively reducing conflict misses.
Data Source
AI summary
Various example embodiments of a processor cache are presented herein. The processor cache may be configured to support redirection of memory blocks between cache lines, including between cache lines in different sets of the processor cache, thereby improving the efficiency of the processor cache by increasing the utilization of the processor cache and reducing cache misses for the processor cache. The redirection of memory blocks between cache lines may include redirection of a memory block from being stored in a first cache line of a first set of the processor cache which is the default set for the memory block (e.g., when the first set does not have any empty cache lines) to a second cache line of a second set of the processor cache which is not the default set for the memory block (e.g., the second set may be any set having at least one empty cache line).