Color-Tagged Cache Write Merging for Lower ECC Overhead
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing cache systems in multi-core coherent systems face challenges in maintaining performance while ensuring fault tolerance due to the introduction of timing overhead from error correcting codes (ECC) in high-speed cache memory, which can lead to data corruption from cosmic rays or malicious memory accesses.
Innovation Solution
Implementing a caching system with a first and second sub-cache in parallel, where the second sub-cache stores write-miss data and includes line type bits and an eviction controller to manage data flushing and eviction based on specific indications, allowing for efficient handling of write-miss data and reducing the need for full ECC checks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correcting codes (ECC) are implemented in high speed cache memory to protect against data corruption, then fault tolerance is improved, but timing overhead increases and cache performance deteriorates
Solution Approach 1:
The cache is divided into multiple ways (e.g., 4-way set associative), where each way has its own ECC protection. This segmentation allows the system to check only the relevant way for a cache access, reducing the timing overhead compared to checking all cache lines, while still providing fault tolerance through ECC in each segment.
Solution Approach 2:
Instead of applying ECC checks to all cache lines on every access (excessive action), the patent applies ECC checks only to the specific way being accessed (partial action). This selective approach reduces timing overhead while maintaining adequate fault tolerance for the actual accessed data.
2Productivity
If cache size is increased to improve performance, then cache hit rate is improved, but access latency increases due to slower cache memory
Solution Approach 1:
The larger cache is organized as a set associative cache with multiple ways, where each way can be accessed independently in parallel. This segmentation allows the system to maintain a larger total cache capacity while keeping access latency low by selecting and accessing only the relevant way, rather than searching through a single large linear array.
Solution Approach 2:
The cache is organized in a multi-dimensional structure with sets and ways, transforming a single-dimensional large cache into a multi-dimensional structure. This allows parallel access to multiple ways within the same cache level, effectively increasing cache capacity without proportionally increasing access latency.
3Productivity
If parallel sub-caches are used to handle write-miss data, then data management efficiency is improved, but device complexity increases
Solution Approach 1:
The second sub-cache serves multiple functions: it handles write-miss data, stores evicted cache lines, and manages dirty bits for write-back operations. This multi-functionality improves data management efficiency by consolidating various cache operations into a single unified structure rather than requiring separate specialized caches for each function.
Solution Approach 2:
The patent merges the functionality of handling write-miss data with the eviction cache functionality into a single second sub-cache. This consolidation reduces the number of separate cache structures needed, managing complexity while maintaining efficient data handling through unified management of write-miss and evicted data.
Data Source
AI summary
Techniques for caching data are provided that include receiving, by a caching system, a write memory command for a memory address, the write memory command associated with a first color tag, determining, by a first sub-cache of the caching system, that the memory address is not cached in the first sub-cache, determining, by second sub-cache of the caching system, that the memory address is not cached in the second sub-cache, storing first data associated with the first write memory command in a cache line of the second sub-cache, storing the first color tag in the second sub-cache, receiving a second write memory command for the cache line, the write memory command associated with a second color tag, merging the second color tag with the first color tag, storing the merged color tag, and evicting the cache line based on the merged color tag.