Memory Controller Prefetching for Row Address Timing Constraints
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Solution Overview
Problem
Computing systems with multiple processing cores experience significant 'dead time' due to memory timing constraints, particularly when consecutive memory requests target different pages, leading to inefficiencies in system memory response.
Innovation Solution
A memory controller that forces prefetches by maintaining the same row address and incrementing the column address, allowing read requests to be serviced from a local cache, thereby reducing idle time and adhering to memory timing constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If consecutive memory requests target different pages, then memory address diversity is improved, but memory device idleness increases due to row address change timing constraints
Solution Approach 1:
The memory controller performs preliminary actions by detecting upcoming row address changes before they occur and initiating prefetch operations in advance. When the controller predicts that a row address change is imminent based on the memory request queue, it prefetches data from the current row before the actual row address change happens, thereby eliminating idle time caused by timing constraints.
Solution Approach 2:
The invention applies beforehand cushioning by creating a buffer of prefetched data that compensates for the upcoming row address change timing constraint. The memory controller monitors the row address change timing constraint and prefetches data beforehand to cushion against the inevitable idle period that would occur when the row address must change, ensuring continuous data availability for memory devices.
2Manufacturing precision
If the memory controller waits for timing constraints to be satisfied, then memory timing accuracy is improved, but system productivity decreases due to dead time
Solution Approach 1:
The memory controller maintains continuity of useful action by continuously prefetching data in the background while monitoring timing constraints. Instead of stopping all operations to wait for timing constraints to be satisfied, the controller continues to service memory requests and simultaneously performs prefetch operations, ensuring that useful actions continue without interruption and eliminating dead time while maintaining timing accuracy.
Solution Approach 2:
The controller performs preliminary prefetch actions during periods when timing constraints are not yet critical, preparing data in advance so that when timing constraints become active, the system can maintain productivity without waiting. This preliminary action allows the system to satisfy timing requirements while keeping memory devices continuously productive.
3Reliability
If the memory controller services requests in strict order, then request processing reliability is improved, but memory utilization decreases due to idle periods
Solution Approach 1:
The memory controller performs preliminary prefetch operations for future requests while maintaining the strict ordering of request processing. By detecting patterns in the request queue and prefetching data in advance of when it will be needed, the controller ensures that data is ready when required for reliable processing, while simultaneously improving memory utilization by keeping memory devices busy with prefetch operations during what would otherwise be idle periods.
Solution Approach 2:
The invention introduces an intermediary prefetch buffer that decouples the strict ordering requirement from memory device utilization. The prefetch buffer acts as an intermediary layer that prepares data in advance according to predicted needs, allowing the memory controller to maintain reliable ordered processing while the memory devices remain continuously utilized through background prefetch operations that don't interfere with the ordered request stream.
Data Source
AI summary
An apparatus having a memory controller is described. The memory controller includes prefetch circuitry to prefetch, from a memory, data having a same row address in response to the memory controller's servicing of its request stream being stalled because of a timing constraint that prevents a change in row address. The memory controller also includes a cache to cache the prefetched data. The memory controller also includes circuitry to compare addresses of read requests in the memory controller's request stream against respective addresses of the prefetched data in the cache and to service those of the requests in the memory controller's request stream having a matching address with corresponding ones of the prefetched data in the cache.