Cache Writeback Circuit for Dirty-Line Eviction Bursts
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Solution Overview
Problem
In computer systems, bursts of memory access requests cause cache misses and evictions, leading to bandwidth contention between read requests and dirty data evictions, resulting in performance reduction for requesting circuits like GPUs.
Innovation Solution
A cache writeback circuit that proactively writes back dirty data to memory during low bandwidth usage, keeping the cache clean and reducing the need for subsequent evictions, thereby avoiding bandwidth contention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dirty data is written back to memory during high bandwidth usage, then data consistency is maintained, but memory bandwidth availability for requesting circuits decreases
Solution Approach 1:
The patent applies preliminary action by proactively writing back dirty data to memory during periods of low bandwidth usage, before subsequent read bursts occur. This advance preparation ensures data consistency is maintained while avoiding bandwidth contention during critical read operations, as the cache is pre-cleaned of dirty lines that would otherwise need to be evicted during read bursts
2Productivity
If cache lines are kept clean by proactive writeback, then bandwidth contention is reduced, but additional memory operations are required
Solution Approach 1:
The patent implements self-service by having the cache writeback circuit autonomously monitor bandwidth usage conditions and automatically initiate writeback operations when appropriate. The circuit detects low bandwidth usage periods and independently performs cache cleaning without requiring external intervention, thereby reducing bandwidth contention during read bursts while minimizing the impact of additional memory operations through intelligent timing
Data Source
AI summary
A cache writeback circuit is disclosed for writing back, without invalidating, dirty cache lines. The cache writeback circuit is configured to enter an active state based on detecting a trigger condition indicative of cache misses to a memory cache circuit within a memory hierarchy of a computer memory subsystem causing cache line eviction activity. During the active state, the cache writeback circuit is configured to identify a set of dirty cache lines in the memory cache circuit, and write back, without invalidating, cache lines of the identified set of dirty cache lines from the memory cache circuit to a memory circuit within a lower level of the memory hierarchy, such as DRAM. The cache writeback circuit may further be configured to identify the dirty cache lines via a cache walk operation, which can be suspended, for example, when a higher-priority cache operation occurs.