L1 Icache Segmentation for Large Program Hit Rate
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Solution Overview
Problem
Small L1 instruction caches are ineffective with large programs due to high rates of misses and low hit rates, as they are size-constrained and cannot accommodate effective instruction prefetching mechanisms.
Innovation Solution
Storing non-instruction information, such as prefetch correlation tables, in a section of the L1 cache to improve prefetching efficiency without increasing cache size, using a multi-way set-associative organization and filter tables to optimize prefetching and reduce unnecessary memory accesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the L1 icache size is increased to improve hit rate with large programs, then the hit rate improves, but the chip area and power consumption increase
Solution Approach 1:
The L1 icache is segmented into multiple ways (e.g., 8 ways), allowing selective activation. The patent activates only the necessary number of ways based on program characteristics, dividing the cache into functional segments that can be independently controlled to reduce area usage while maintaining hit rate.
Solution Approach 2:
The patent dynamically adjusts the number of active cache ways based on program behavior analysis. By monitoring program characteristics and adapting the active cache configuration in real-time, the system optimizes the balance between hit rate and area consumption without static over-provisioning.
2Reliability
If the L1 icache size is increased to accommodate more instructions for large programs, then the effectiveness improves, but the power consumption increases
Solution Approach 1:
The L1 icache is divided into multiple independent ways that can be individually powered on or off. This segmentation allows the system to activate only the necessary portion of the cache based on program requirements, reducing power consumption while maintaining effectiveness for large programs.
Solution Approach 2:
The patent changes the operational parameters of the L1 icache by dynamically adjusting the number of active ways based on program characteristics. This parameter adjustment optimizes the balance between cache effectiveness and power consumption without requiring a fixed large cache configuration.
3Area of stationary object
If a small L1 icache is used to save area and power, then area and power are reduced, but the hit rate with large programs deteriorates
Solution Approach 1:
The patent implements dynamic configuration of the L1 icache, adjusting the number of active ways based on program characteristics. This dynamic approach allows a physically smaller cache to achieve the performance of a larger cache by optimizing resource allocation in real-time, improving hit rate without increasing area.
Solution Approach 2:
The L1 icache is designed to serve multiple program sizes and types effectively through multi-way organization and dynamic activation. The same cache structure can adapt its configuration to handle both small and large programs optimally, providing universal performance across different workload types without requiring multiple specialized caches.
Data Source
AI summary
The hit rate of a L1 icache when operating with large programs is substantially improved by reserving a section of the L1 icache for regular instructions and a section for non-instruction information. Instructions are prefetched for storage in the instruction section of the L1 icache based on information in the non-instruction section of the L1 icache.