Memory Request Queue Lookahead Priority Elevation for Stall Avoidance
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Solution Overview
Problem
In multi-core System on Chip (SoC) architectures, managing memory access among multiple requesters is challenging due to priority conflicts that can lead to stalls and reduced performance, particularly when lower priority requests are stalled while higher priority requests are pending.
Innovation Solution
Implementing a priority elevation mechanism that allows high priority requests to elevate the priority of all older requests in the memory system, using a hierarchical lookahead priority collection mechanism to manage memory access across multiple cores, ensuring critical transactions are prioritized effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a priority scheme is used to manage memory access among multiple requesters, then memory access ordering is improved, but performance is reduced due to stalls when lower priority requests block higher priority requests
Solution Approach 1:
The patent implements a lookahead mechanism that examines future high-priority requests before they are fully processed. When a high-priority request is detected in the pipeline, the system proactively elevates the priority of older pending requests, preventing stalls before they occur. This preliminary action resolves the contradiction by maintaining both proper memory ordering and high performance.
2Stability of the object's composition
If lower priority requests are processed before higher priority requests, then memory access ordering is maintained, but data throughput is reduced due to unnecessary stalls
Solution Approach 1:
The lookahead priority collection mechanism detects high-priority requests in advance and triggers priority elevation before the stalled request can block the pipeline. This allows the system to maintain memory ordering while preventing throughput degradation by proactively resolving potential conflicts.
3Productivity
If priority elevation is implemented to resolve stalls, then performance is improved, but device complexity increases due to additional priority management mechanisms
Solution Approach 1:
The lookahead mechanism uses a simple buffer to store priority information from future requests. When a high-priority request is detected, the system elevates priorities of older requests based on this pre-collected information. This approach improves performance while minimizing complexity by using a straightforward buffering and comparison mechanism.
Solution Approach 2:
The patent introduces a lookahead priority collection mechanism as an intermediary layer between the memory request pipeline and the arbitration logic. This mediator collects priority information in advance and provides it to the arbitration unit, simplifying the overall priority management while enabling performance improvements.
4Reliability
If critical transactions are prioritized using traditional methods, then responsiveness is improved, but stalls occur when lower priority requests are pending
Solution Approach 1:
The lookahead mechanism proactively identifies high-priority transactions before they enter the critical path. When such transactions are detected, the system elevates the priority of older pending requests, ensuring that critical transactions can proceed without stalls while maintaining proper ordering. This eliminates wait time for critical operations.
Data Source
AI summary
A queuing requester for access to a memory system is provided. Transaction requests are received from two or more requestors for access to the memory system. Each transaction request includes an associated priority value. A request queue of the received transaction requests is formed in the queuing requester. Each transaction request includes an associated priority value. A highest priority value of all pending transaction requests within the request queue is determined. An elevated priority value is selected when the highest priority value is higher than the priority value of an oldest transaction request in the request queue; otherwise the priority value of the oldest transaction request is selected. The oldest transaction request in the request queue with the selected priority value is then provided to the memory system. An arbitration contest with other requesters for access to the memory system is performed using the selected priority value.