Parallel Snoop Hazard Checking Interconnect Circuitry
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Solution Overview
Problem
As system-on-chip integrated circuits increase in complexity, the interconnect circuitry faces challenges in efficiently communicating access transactions while preventing hazards like transaction ordering violations and coherence breakdowns, leading to increased latency and energy consumption.
Innovation Solution
The interconnect circuitry incorporates buffer circuitry for transaction buffering and reordering, hazard checking circuitry for enforcing a predetermined order, and snoop circuitry with reordering capabilities to manage coherence, allowing snoop operations to be performed in parallel with hazard checking, thereby reducing latency and improving system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hazard checking is performed sequentially before snoop operations, then transaction ordering is ensured, but latency increases
Solution Approach 1:
The hazard checking circuitry performs hazard checks on access transactions in advance, before snoop operations are completed. The reorder buffer holds transactions while hazard checking is performed, allowing snoop operations to proceed in parallel without compromising transaction ordering. This preliminary hazard checking enables subsequent snoop operations to be executed concurrently, reducing overall latency while maintaining reliability.
Solution Approach 2:
The patent introduces a temporal dimension by overlapping hazard checking and snoop operations in time. The reorder buffer enables hazard checking to occur while snoop operations are in progress, transforming the traditional sequential execution into a parallel process. This dimensional change allows both operations to proceed simultaneously, reducing latency without sacrificing transaction ordering guarantees.
2Loss of time
If snoop operations are performed in parallel with hazard checking, then latency is reduced, but system complexity increases
Solution Approach 1:
The interconnect circuitry is segmented into distinct functional units: hazard checking circuitry, snoop circuitry, and a reorder buffer. This segmentation allows each component to operate independently and in parallel, reducing latency while managing complexity through modular design. The hazard checking circuitry processes transactions, the reorder buffer manages ordering, and the snoop circuitry handles coherence, with each segment performing its specific function without interfering with others.
Solution Approach 2:
The reorder buffer acts as an intermediary between the hazard checking circuitry and the snoop circuitry. It receives access transactions from the hazard checking circuitry, holds them during parallel snoop operations, and ensures proper ordering is maintained. This intermediary component enables parallel operation of hazard checking and snoop circuitry while maintaining system coherence and transaction ordering, effectively managing the complexity introduced by parallel processing.
3Loss of time
If speculative snoop processing is performed, then latency is hidden, but risk of erroneous operation increases
Solution Approach 1:
The hazard checking circuitry performs preliminary hazard checks on access transactions before they are passed to the snoop circuitry. This preliminary validation ensures that only transactions that have passed hazard checking enter the speculative snoop processing pipeline, reducing the risk of erroneous operations. The reorder buffer then holds these validated transactions while snoop operations complete, allowing speculative execution to proceed safely.
Solution Approach 2:
The system implements feedback mechanisms where snoop responses are returned to the reorder buffer, which then determines when transactions can be safely issued. The reorder buffer monitors the completion of snoop operations and ensures that transactions are issued only after appropriate coherence checks are satisfied. This feedback loop maintains reliability by validating speculative snoop processing results before committing them to the system.
Data Source
AI summary
A system-on-chip integrated circuitry includes interconnect circuitry for connecting transaction sources with transaction destinations. A buffer circuit buffers a plurality of access transactions received from the transaction sources before they are passed on to respective transaction destinations. Hazard checking circuitry, such as identifier reuse circuitry, performs hazard checks for access transactions in parallel with snoop operations performed by snoop circuitry for managing coherence between data values stored within the plurality of cache memories. The snoop circuitry includes snoop reordering circuitry for permitting reordering of snoop responses. The snoop circuitry may issue a snoop request for a given access transaction in parallel with the hazard checking circuitry performing one or more hazard checks for that transaction.