Victim cache

Definition

A victim cache is a small, secondary cache used to store blocks that have been evicted from a primary cache in order to minimize cache misses. This mechanism allows for better utilization of cache memory by retaining recently discarded data, which may still be relevant for future access. It plays a crucial role in improving the efficiency of non-blocking caches, where multiple memory accesses can occur simultaneously without stalling the processor.

5 Must Know Facts For Your Next Test

1. The victim cache temporarily holds evicted cache lines from the primary cache, making it easier to retrieve recently used data without going back to main memory.
2. It typically has a smaller size than the primary cache and can be implemented as a fully associative cache to increase flexibility in data retrieval.
3. Victim caches are particularly beneficial in workloads with high locality of reference, where data is often reused shortly after being evicted.
4. They can help reduce the negative impact of conflict misses by storing evicted blocks that might be needed again soon.
5. The effectiveness of a victim cache is highly dependent on its size and associativity, which should be carefully designed to balance performance with cost.

Review Questions

• How does a victim cache improve the performance of non-blocking caches in handling memory requests?
  • A victim cache enhances the performance of non-blocking caches by retaining recently evicted data that might still be relevant for future accesses. Since non-blocking caches allow multiple memory requests to proceed simultaneously, having a victim cache means that if an accessed block was recently evicted, it can quickly be retrieved from the victim cache instead of going all the way back to main memory. This helps reduce latency and overall stall times during multi-request processing.
• Discuss the impact of conflict misses on primary caches and how victim caches help mitigate this issue.
  • Conflict misses occur when multiple data blocks compete for the same cache line in a primary cache. Victim caches help alleviate this problem by providing a temporary storage area for recently evicted blocks, which may still be needed. By storing these blocks, a victim cache allows for quick retrieval without requiring another access to main memory. This mechanism not only reduces conflict misses but also improves the efficiency of memory access patterns.
• Evaluate how the design choices related to size and associativity of a victim cache can influence overall system performance.
  • The design choices regarding the size and associativity of a victim cache have significant implications for system performance. A larger victim cache can store more evicted blocks, potentially reducing misses; however, it also consumes more resources and may increase access times. On the other hand, higher associativity can enhance retrieval flexibility, allowing more efficient management of stored blocks but may complicate the implementation and slow down lookups. Striking the right balance between these factors is crucial for optimizing performance while minimizing costs.

Related terms

cache hit: A situation where the data requested by the processor is found in the cache memory, resulting in faster access.

cache miss: An event that occurs when the data requested by the processor is not found in the cache, requiring a fetch from slower main memory.

non-blocking cache: A type of cache that allows multiple memory requests to be processed concurrently, reducing stalls and improving overall system performance.