Concurrent Dirty Bit Access in Associative Cache
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Solution Overview
Problem
Conventional cache flushing and rinsing processes are inefficient due to serial access methods, which slow down the process of writing back dirty cache lines to main memory, especially in n-way associative caches where only one address can be probed at a time.
Innovation Solution
Implementing a system that allows concurrent or parallel access to dirty bits associated with multiple ways of a cache index, enabling simultaneous reading and writing of dirty bits, particularly in n-way associative caches using flip-flops or memory arrays with multiple ports, thereby speeding up the flush and rinse operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If serial access methods are used to probe cache ways, then device complexity is reduced, but productivity of cache flushing and rinsing operations deteriorates
Solution Approach 1:
The cache ways are divided into multiple groups, with each group assigned to a separate port. This segmentation allows parallel access to multiple ways simultaneously through different ports, increasing flushing and rinsing productivity without requiring a completely new access architecture.
Solution Approach 2:
The patent introduces a new dimension of parallelism by adding multiple access ports to the cache structure. Instead of improving serial access speed, the solution moves to parallel access across multiple ports, each handling a subset of cache ways, thereby achieving n-times speedup for n-way associative caches.
2Loss of time
If serial access methods are used to probe cache ways, then device complexity is reduced, but loss of time in cache operations increases
Solution Approach 1:
Cache ways are segmented into groups assigned to different ports, enabling simultaneous probing of multiple ways. This reduces the time required to identify dirty lines from O(n) sequential probes to O(1) parallel probes, significantly reducing cache operation latency.
Solution Approach 2:
The patent performs preliminary parallel probing of all cache way groups to identify dirty lines before initiating the flush or rinse operation. This preliminary identification step, executed concurrently across all ports, eliminates sequential search delays and prepares the system for efficient dirty line handling.
3Productivity
If concurrent access to dirty bits is implemented, then productivity of cache operations improves, but device complexity increases
Solution Approach 1:
The dirty bit storage is segmented into multiple groups, with each group accessible through a separate port. This allows concurrent reading of dirty bits from different cache way groups simultaneously, improving dirty bit access productivity while keeping each port's circuit complexity manageable.
Solution Approach 2:
Each port is designed with universal functionality to handle both data access and dirty bit reading operations. This multi-functionality allows the same port infrastructure to serve multiple purposes, improving productivity without proportionally increasing overall circuit complexity.
Data Source
AI summary
The present application describes embodiments of a method and apparatus for concurrently accessing dirty bits in a cache. One embodiment of the apparatus includes a cache configurable to store a plurality of lines. The lines are grouped into a plurality of subsets the plurality of lines. This embodiment of the apparatus also includes a plurality of dirty bits associated with the plurality of lines and first circuitry configurable to concurrently access the plurality of dirty bits associated with at least one of the plurality of subsets of lines.