Prefetch Throttling Circuitry for Interconnect Congestion Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern processing devices face performance bottlenecks due to significant bandwidth consumption by prefetch transactions in interconnects, leading to congestion and inefficient data retrieval, as existing prefetch mechanisms do not effectively manage congestion in communication paths.
Innovation Solution
An apparatus and method that utilize congestion tracking circuitry to maintain congestion indications for each route in the interconnect, allowing prefetch throttling circuitry to determine whether to issue prefetch transactions based on congestion levels and confidence indications, thereby adaptively managing prefetch transactions to avoid oversubscribing bottlenecks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prefetch transactions are issued to retrieve data into local caches, then cache hit ratio is improved, but interconnect bandwidth consumption increases
Solution Approach 1:
The system dynamically changes the parameters of prefetch transactions by assigning different priorities (high, medium, low) based on confidence indications and interconnect congestion levels. This allows the prefetch mechanism to adapt its behavior to current system conditions, reducing bandwidth consumption during congested periods while maintaining cache hit ratio by prioritizing high-confidence prefetches.
Solution Approach 2:
The system implements feedback mechanisms where congestion indications are monitored and used to adjust prefetch transaction issuance. The congestion tracking circuitry provides feedback about interconnect utilization, which the prefetch throttling circuitry uses to modulate prefetch rates, creating a closed-loop control system that balances cache performance with interconnect bandwidth management.
2Speed
If multiple prefetch transactions are issued simultaneously, then data retrieval speed is improved, but interconnect congestion increases
Solution Approach 1:
The system dynamically adjusts the rate and priority of prefetch transactions based on real-time interconnect congestion conditions. Rather than issuing prefetches at a fixed rate, the system modulates prefetch issuance dynamically, increasing rates when bandwidth is available and reducing rates when congestion is detected, thereby maintaining data retrieval speed while avoiding excessive congestion.
Solution Approach 2:
The system segments prefetch transactions into different priority levels (high, medium, low) based on confidence indications. This segmentation allows the interconnect to handle prefetches in priority order, ensuring that high-confidence prefetches are issued even during congestion while lower-confidence prefetches are deferred, thus maintaining overall data retrieval performance without overwhelming the interconnect.
3Quantity of substance
If prefetch transactions are throttled during congestion, then interconnect bandwidth is optimized, but cache hit ratio may decrease
Solution Approach 1:
The system applies different quality levels of prefetching to different data access patterns by using confidence indications. High-confidence prefetches (those with high local quality/likelihood of being used) are maintained even during congestion, while low-confidence prefetches are throttled. This ensures that the most valuable prefetches continue to improve cache hit ratio while bandwidth is optimized by reducing less valuable prefetches.
Solution Approach 2:
The system changes the priority parameter of prefetch transactions based on confidence indications and congestion levels. During congestion, instead of uniformly throttling all prefetches, the system adjusts priorities dynamically, maintaining high-priority prefetches that are most likely to improve cache hit ratio while reducing low-priority prefetches, thus optimizing bandwidth without significantly impacting cache performance.
4Productivity
If congestion tracking circuitry is implemented, then prefetch management is improved, but device complexity increases
Solution Approach 1:
The congestion tracking circuitry is designed to serve multiple functions: it monitors interconnect utilization, provides congestion indications to prefetch throttling logic, and can be used for priority arbitration. By making the congestion tracking mechanism universal and multi-functional, the patent reduces overall system complexity while improving prefetch management efficiency, as the same circuitry supports multiple aspects of interconnect management rather than requiring separate dedicated circuits for each function.
Data Source
AI summary
An apparatus and method are provided for managing prefetch transactions. The apparatus has an interconnect for providing communication paths between elements coupled to the interconnect. The elements coupled to the interconnect comprise at least a requester element to initiate transactions, and a plurality of completer elements each of which is arranged to respond to a transaction received by that completer element. Congestion tracking circuitry maintains, in association with the requester element, a congestion indication for each of a plurality of routes through the interconnect used to propagate transactions initiated by that requester element. Each route comprises one or more communication paths, and the route employed to propagate a given transaction is dependent on a target completer element for that transaction. Prefetch throttling circuitry then identifies, in response to an indication of a given prefetch transaction that the requester element wishes to initiate, the target completer element amongst the plurality of completer elements to which that given prefetch transaction would be issued. It then determines whether to issue the given prefetch transaction in dependence on the congestion indication for the route that has been determined.