Memory Read Honor Circuit Selective Prefetch Bandwidth
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Solution Overview
Problem
In processor-based systems, speculative memory prefetching often leads to cache pollution and increased memory access latency due to inaccurate or untimely prefetch requests, which can worsen CPU performance and memory system contention.
Innovation Solution
A memory read honor circuit is introduced to selectively honor speculative memory prefetch requests based on the bandwidth constraints of the memory access path, determining if requested data will be forwarded only if the bandwidth state meets a defined threshold, thereby conserving memory access bandwidth and improving CPU performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If speculative memory prefetch requests are honored to reduce memory access latency, then CPU performance improves, but cache pollution increases and memory system bandwidth is consumed
Solution Approach 1:
The system changes the parameter of request prioritization by introducing request modes (required vs. preferred) and selectively honoring prefetch requests based on bandwidth state. This allows the memory system to adjust which requests are fulfilled based on current conditions, reducing cache pollution while maintaining performance benefits.
Solution Approach 2:
The memory read honor circuit dynamically adjusts prefetch request fulfillment based on real-time bandwidth state monitoring. When bandwidth is constrained, the system dynamically stops honoring preferred prefetch requests, allowing the system to adapt to changing workload conditions and avoid cache pollution.
2Loss of time
If speculative memory prefetch requests are honored to reduce memory access latency, then CPU performance improves, but memory system bandwidth is consumed
Solution Approach 1:
The system dynamically monitors bandwidth state and adjusts prefetch request fulfillment in real-time. When bandwidth is available, preferred requests are honored; when bandwidth is constrained, they are dropped. This dynamic adaptation allows the system to maintain performance benefits without permanently consuming excessive bandwidth.
Solution Approach 2:
The system changes the parameter of request fulfillment based on bandwidth availability. By introducing selective honoring logic that responds to bandwidth state, the system adjusts the effective request queue behavior to balance performance improvement against bandwidth consumption.
3Productivity
If aggressive data prefetching is used to hide memory access latency, then CPU workload performance improves, but memory system contention increases
Solution Approach 1:
The system changes the parameter of prefetch request fulfillment based on memory system state. By monitoring bandwidth availability and adjusting which requests are honored, the system reduces contention while maintaining the performance benefits of prefetching during low-contention periods.
Data Source
AI summary
Selective honoring of speculative memory-prefetch requests based on bandwidth constraint of a memory access path component(s) in a processor-based system. To reduce memory access latency, a CPU includes a request size in a memory read request of requested data to be read from memory and a request mode of the requested data as required or preferred. A memory access path component includes a memory read honor circuit configured to receive the memory read request and consult the request size and request mode of requested data in the memory read request. If the selective prefetch data honor circuit determines that bandwidth of the memory system is less than a defined bandwidth constraint threshold, then the memory read request is forwarded to be fulfilled, otherwise, the memory read request is downgraded to only include any requested required data.