Enhanced DWRR Arbiter for Hardware Access Scheduling
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Solution Overview
Problem
Existing arbiters in high-performance computing systems fail to ensure long-term fairness, accommodate variable-sized bursts, define weights with sufficient granularity, are easy to implement, allow immediate access to hardware resources, and rotate between requesters evenly, particularly due to issues with latency and resource allocation in systems like DWRR arbiters.
Innovation Solution
An enhanced DWRR arbiter that associates each requester with a credit counter and weight, granting access based on specific conditions and replenishing credits dynamically to allow multiple chances for requesters to access resources, thereby improving fairness and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional arbiters (RR, WRR, DWRR) are used for scheduling hardware accesses, then implementation simplicity is maintained, but long-term fairness and rotation evenness deteriorate
Solution Approach 1:
The arbiter is segmented into multiple independent components: a rotation manager that tracks service rounds for each requester, a credit counter for each requester, and a scheduling logic that combines both mechanisms. This segmentation allows the system to achieve long-term fairness through rotation tracking while maintaining simplicity through modular design.
Solution Approach 2:
The system performs preliminary actions by pre-allocating credit counters to each requester based on their weight before arbitration begins. This preliminary credit allocation, combined with pre-tracking of service rounds, enables the arbiter to make fair scheduling decisions without complex real-time calculations, thus improving reliability while keeping implementation manageable.
2Reliability
If credit counters are replenished only after all requesters are served, then fairness is maintained, but access latency increases
Solution Approach 1:
The credit replenishment mechanism is made dynamic: instead of a fixed post-service replenishment, the system continuously tracks service rounds and replenishes credits based on current arbitration state. Requesters whose turn comes up in the rotation can access resources as soon as their credit counter allows, reducing latency while maintaining fairness through the rotation framework.
Solution Approach 2:
The arbiter implements feedback by continuously monitoring the service round counter and credit counter states. When a requester's service round is reached and credits are available, immediate access is granted. The system feedback loop ensures that credit replenishment timing is optimized based on actual arbitration needs, balancing fairness and latency.
3Adaptability or versatility
If weights are assigned to proportion traffic, then traffic distribution is improved, but granularity and precision in weight definition are insufficient
Solution Approach 1:
The system changes the parameter representation by using weighted credit counters instead of simple integer weights. Each requester is assigned a weight that determines the proportion of credits replenished to their counter. This parameter transformation enables fine-grained traffic proportioning with sufficient precision, as credit counters can represent fractional weight allocations through their cumulative credit accumulation.
4Productivity
If the arbiter grants access immediately when conditions are met, then productivity is improved, but rotation evenness and fairness deteriorate
Solution Approach 1:
The rotation manager acts as an intermediary between the credit counter and the access grant decision. Even when a requester has sufficient credits, the rotation manager ensures that the requester is granted access only when their service round is reached, maintaining rotation evenness. This intermediary mechanism reconciles the conflict between immediate access (productivity) and fair rotation (reliability).
Data Source
AI summary
In one embodiment, a method by an arbiter associated with hardware resources of a computing system includes associating with N indexed requesters requesting accesses to the hardware resources, where each of the N indexed requesters is associated with a credit counter and a weight, repeatedly granting a right to access the hardware resources to each requester that satisfies conditions in an indexing order among the N indexed requesters until none of the N indexed requesters satisfies the conditions and replenishing, upon a determination that none of the N indexed requesters satisfies the conditions, a credit counter associated with each of the N indexed requesters.