Set-Associative Cache Controller Pipeline for Faster Status Updates
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Solution Overview
Problem
Highly parallel data applications experience pipeline stalls due to cache access inefficiencies, leading to decreased processor performance, despite increased cache sizes and operating frequencies.
Innovation Solution
Implementing a cache controller with a multi-stage pipeline that performs tag comparisons and updates cache set status information in the same pipeline stage, using flip-flop circuits for the cache set status array to reduce access times and power consumption, and delaying status updates to subsequent stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cache size is increased to reduce cache misses, then cache hit rate is improved, but access time and power consumption increase
Solution Approach 1:
The cache controller is divided into multiple pipeline stages (first stage for tag comparison, second stage for status update) that operate concurrently. Different cache sets are processed in parallel across these stages, allowing the system to maintain high cache hit rates while reducing effective access time through pipelined operation.
Solution Approach 2:
The status array is updated in the second pipeline stage using status information generated in the first stage, before the next memory access request arrives. This preliminary updating ensures that when a new request comes in, the status information is already current, reducing the effective access time without compromising cache hit rate.
2Reliability
If cache size is increased to reduce cache misses, then cache hit rate is improved, but power consumption increases
Solution Approach 1:
The cache controller is segmented into pipeline stages with flip-flop-based status arrays that can be updated independently. This segmentation allows power-efficient updating of only the necessary status information rather than refreshing entire cache structures, maintaining high cache hit rates while reducing overall power consumption.
Solution Approach 2:
The patent changes the implementation parameter of the status array from traditional memory cells to flip-flop circuits in the second pipeline stage. This parameter change reduces power consumption for status maintenance while preserving the ability to track cache hit rates effectively.
3Productivity
If multi-stage pipeline is implemented to process memory requests, then throughput is improved, but complexity of cache controller increases
Solution Approach 1:
The cache controller is segmented into two main pipeline stages: tag comparison in the first stage and status array updating in the second stage. This segmentation enables concurrent processing of multiple memory requests, improving throughput while keeping each individual stage relatively simple and manageable.
Solution Approach 2:
The pipeline structure is designed to handle multiple types of operations (tag comparison, status updating, cache hit/miss determination) within a universal multi-stage framework. This multi-functionality allows the same pipeline structure to process various memory access patterns, improving throughput without proportionally increasing complexity.
4Reliability
If status array is updated immediately after tag comparison, then cache coherence is maintained, but pipeline stalls occur
Solution Approach 1:
The cache controller operations are segmented into distinct pipeline stages: tag comparison in the first stage and status array updating in the second stage. This segmentation allows tag comparisons to proceed without waiting for status updates, maintaining cache coherence while preventing pipeline stalls and improving overall throughput.
Solution Approach 2:
Status array updates are performed as a preliminary action in the second pipeline stage using information from the first stage, rather than blocking the first stage to perform updates immediately. This maintains cache coherence while keeping the pipeline flowing continuously, improving throughput.
Data Source
AI summary
An apparatus and method for efficiently processing cache accesses of an integrated circuit. In various implementations, a computing system includes a cache with a tag array, a cache controller, and a data array. The cache controller includes a cache set status array. The cache set status array stores data using any of a variety of flip-flop circuits, which reduces access times and power consumption compared to random access memory (RAM) cells. In each pipeline stage prior to updating the cache set status array, the cache controller conditionally updates cache set status values based on comparisons between a selected set of the memory access request with a set of a previous memory access request that has not yet updated the status array. Updates of cache status values based on the tag comparison occur in the second pipeline stage, which allows reduction of the clock cycle.