Cache Controller Stack Pointer Locking Mechanism
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Solution Overview
Problem
Modern processor systems face performance degradation due to cache eviction, which can lead to slower access times for frequently accessed data, such as the program stack, as the cache line containing the stack top may be evicted using the least-recently-used (LRU) algorithm.
Innovation Solution
A cache system with a cache controller that receives the stack pointer, stores a cache line containing the contents of a specific address range in main memory including the stack pointer, and locks this cache line to prevent eviction, ensuring that the stack top remains in the cache for faster access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cache uses LRU algorithm for eviction, then cache management is automated and efficient for general cases, but the stack top data may be evicted causing performance degradation
Solution Approach 1:
The patent applies local quality by treating the stack top cache line differently from other cache lines. Specifically, it sets the write-back inhibit bit for the cache line containing the stack pointer, preventing its eviction from the cache. This localized special treatment ensures that critical stack data remains in cache while other data follows standard LRU eviction policies, thus resolving the contradiction between automated cache management and reliable stack data access.
2Speed
If the cache line containing stack pointer is locked to prevent eviction, then stack access speed is improved, but cache flexibility and eviction capability are reduced
Solution Approach 1:
The patent implements local quality by applying the lock bit only to the specific cache line containing the stack pointer, rather than locking all cache lines. This selective locking approach maintains cache flexibility for other data while ensuring fast stack access. The write-back inhibit bit is set only for the relevant cache line, allowing the cache to dynamically manage other lines according to LRU policy.
Solution Approach 2:
The patent applies dynamics by making the cache line locking status changeable based on the stack pointer location. As the stack pointer moves to different memory addresses, different cache lines are selectively locked or unlocked. This dynamic adaptation allows the cache to maintain flexibility while providing consistent fast access to the current stack top location.
3Reliability
If more cache lines are locked to protect frequently accessed data, then cache hit rate is improved, but the number of evictable lines decreases reducing cache utility
Solution Approach 1:
The patent applies local quality by selectively locking only the cache line containing the stack pointer using the write-back inhibit bit, rather than locking multiple cache lines or implementing complex locking mechanisms. This minimal selective locking achieves high cache hit rates for stack operations while maintaining simple cache management and preserving cache utility for other data.
Data Source
AI summary
A cache system is provided for system with a CPU and memory. The CPU has a stack pointer register for storing a stack pointer. The stack pointer represents an address in main memory at the top of the stack. The cache system has a cache RAM structured into cache lines and cache controller circuitry. The cache controller circuitry is operable to: receive the stack pointer, store a first cache line containing the contents of a first address range of bytes of the main memory, the first address range including the stack pointer; and lock the first cache line to protect the first cache line from cache eviction.