Link Interface Optimization Logic for Bus Throughput
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Solution Overview
Problem
Modern bus interfaces in computer systems face performance issues due to bandwidth limitations, where optimization techniques that reorder data transfer requests can introduce latency, especially when the bus is not heavily loaded, and backpressure is not a reliable indicator of when optimization is advantageous, particularly in bifurcated buses like PCI Express.
Innovation Solution
Implementing link interface circuits with a metering system that measures and predicts bus activity levels to dynamically enable or disable optimization logic based on performance metrics such as response time and throughput, allowing for optimized data transfer request handling only when the bus is congested, using a request selection circuit and optimization control circuit that computes a performance metric to determine the optimal operating mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optimization logic is always enabled to improve bus efficiency, then throughput is improved under high load, but latency increases during low activity periods
Solution Approach 1:
The patent implements dynamic switching between optimization modes based on real-time bus activity measurement. The metering circuit continuously monitors bus utilization, and the control logic dynamically enables or disables optimization logic accordingly. This resolves the contradiction by making the system adaptive: optimization is activated only when bus activity exceeds a threshold, improving throughput during high load while minimizing latency during low activity periods.
2Speed
If reordering requests is performed to improve memory access efficiency, then memory access time is reduced, but latency at the bus interface stage increases
Solution Approach 1:
The patent changes the operational parameter of the bus interface by switching between optimization enabled/disabled states based on bus activity metrics. When optimization is enabled, requests are reordered to improve memory access patterns (improving memory access time). When disabled, requests pass through immediately (reducing bus interface latency). This parameter change resolves the contradiction by optimizing for the right metric at the right time based on system conditions.
3Productivity
If optimization circuits wait to collect multiple requests before reordering, then bus efficiency improves, but latency is added to individual requests
Solution Approach 1:
The patent applies partial optimization by enabling reordering only when sufficient requests are available to justify the latency overhead. The metering circuit determines whether bus activity level warrants activation of optimization logic. This partial action approach resolves the contradiction by applying optimization selectively - full optimization effort is deployed only when it will benefit overall bus efficiency, otherwise requests are transmitted with minimal delay.
Data Source
AI summary
Optimization logic that optimizes a stream of requests being transmitted onto a link by a link interface unit can be enabled or disabled based on a performance metric that represents a measure of the degree to which a response to a request is likely to be slowed due to congestion, propagation delays, or other bottlenecks in the system. For example, the performance metric can be based on a measured level of link activity due to requests from the transmitting device and/or a prediction as to behavior (e.g., access time) of the target device that receives the stream of requests. The control logic advantageously does not require extra signals to be carried on the bus.