Rate Limiter Circuits for Virtual Channel Bandwidth Allocation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In digital systems, shared interconnects can become bottlenecks, leading to high latency and low bandwidth for critical agents due to excessive traffic from non-critical agents, which can impact the performance of latency-sensitive transactions like isochronous data transmission.

Innovation Solution

Implementing rate limiter circuits that control the transmission rate in virtual channels, using a 'leaky bucket' mechanism to manage bandwidth and prioritize critical agents by adjusting rate limits based on the power state of critical agents, ensuring sufficient bandwidth and latency for critical transactions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple virtual channels share the same physical interconnect, then bandwidth utilization is improved, but latency for critical agents deteriorates due to traffic from non-critical agents

Engineering Contradiction:

Improvebandwidth utilizationVSAvoidlatency for critical agents

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent implements dynamic rate limiting that adjusts transmission rates based on real-time conditions. Rate limiters monitor traffic patterns and dynamically modify the transmission rates of non-critical agents to prevent them from overwhelming critical agents, thereby maintaining low latency while preserving high bandwidth utilization through adaptive resource allocation

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes operational parameters by adjusting rate limits for different virtual channels based on traffic conditions and agent criticality. By modifying transmission rate parameters dynamically, the system optimizes the balance between overall bandwidth utilization and latency performance for critical transactions

Inventive Principle:

Principle #35Parameter changes

2Loss of time

If rate limiting is applied to non-critical agents, then latency for critical agents is improved, but overall bandwidth utilization deteriorates

Engineering Contradiction:

Improvelatency for critical agentsVSAvoidoverall bandwidth utilization

Core Design Contradiction:

Loss of timeVSProductivity

Solution Approach 1:

The rate limiting mechanism is designed to be dynamic rather than static. Rate limits for non-critical agents are adjusted in real-time based on system conditions, allowing the system to maintain high overall bandwidth utilization while ensuring critical agents experience low latency. When critical agents need bandwidth, rate limits are tightened; when conditions permit, rate limits are relaxed to maximize utilization

Inventive Principle:

Principle #15Dynamics

3Device complexity

If arbitration treats all virtual channels equally, then device complexity is reduced, but performance for critical transactions deteriorates

Engineering Contradiction:

Improvearbitration complexityVSAvoidlatency for critical transactions

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The arbitration system implements local quality differentiation by applying different rate limiting policies to different virtual channels based on their criticality. Critical agents receive preferential treatment with higher rate limits and priority access, while non-critical agents receive stricter rate limiting. This localized differentiation maintains relatively simple arbitration logic while significantly improving performance for critical transactions

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11513848B2Critical agent identification to modify bandwidth allocation in a virtual channel

Publication Date: 2022.11.29 APPLE INC

AI summary

In an embodiment, a system includes rate limiter circuits corresponding to various agents that issue transactions in a virtual channel. At least one agent may be identified as a critical agent, and different rate limits (e.g., lower limits) may be selected for other agents when the critical agent is on than when the critical agent is off (e.g., higher limits).