Circular Topology Node Reservation Mechanism Preventing Starvation
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Solution Overview
Problem
In semiconductor computer chips with multiple processing nodes connected in a circular topology, there is a potential for node starvation due to token constraints, where processing nodes may be prevented from transmitting messages if upstream nodes consume destination processing node's tokens before they can propagate to starved nodes.
Innovation Solution
An anti-starvation reservation mechanism is implemented, which separates processing nodes into partition groups and enforces a reservation policy that allows nodes to send reservations only when their assigned partition group is active. This mechanism uses an additional bus to increment a global partition counter, ensuring that only active partition groups can transmit token reservation requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If token constraints are implemented to manage message transmission between processing nodes, then message transmission control is improved, but node starvation occurs when upstream nodes consume destination tokens before they can propagate to starved nodes
Solution Approach 1:
The system segments processing nodes into different partition groups (e.g., Group 0, Group 1) and assigns each group specific time windows during which they can transmit reservation requests. This segmentation prevents all nodes from competing simultaneously for tokens, eliminating starvation while maintaining transmission control.
Solution Approach 2:
The system implements periodic time windows that alternate between different partition groups. Each group is granted exclusive transmission opportunities during its assigned time window, creating a periodic pattern that ensures fair token distribution and prevents starvation of any particular node.
2Reliability
If reservation mechanisms are added to prevent node starvation, then fairness among nodes is improved, but device complexity increases due to additional buses and partition management
Solution Approach 1:
The partition counter and time window mechanism serve multiple functions: they control reservation request timing, manage partition group activation, and coordinate token distribution across all nodes. This multi-functionality reduces the need for separate dedicated control structures, mitigating the increase in device complexity.
3Reliability
If partition groups are assigned to processing nodes with active phases, then node starvation is prevented, but time delay increases due to waiting for active partition phase
Solution Approach 1:
Nodes submit reservation requests during inactive phases in advance, and these requests are queued for processing during the next active phase. This preliminary action allows nodes to prepare transmission requests without immediate execution, preventing starvation while minimizing actual waiting time for data transmission.
Data Source
AI summary
A computer chip, a method, and computer program product for managing reservation between processing nodes with token constraints. The computer chip includes a plurality of processing nodes interconnected in an on-chip data transfer network configured in a circular topology. The processing nodes include a reservation mechanism that manages reservations made by the processing nodes. The reservation mechanism applies a reservation policy when a starvation condition is met on a processing node. The reservation policy separates the processing nodes into partition groups and dictates that a processing node may only send a reservation when their assigned partition group is active. Each of the processing nodes includes a buffer for storing messages that is divided into a pool of tokens and a pool of reservation tokens. The tokens are used for standard message transmission and the reservation tokens are reserved for token reservation requests received at a destination node.