Cache Pipeline Arbitration for Priority Transaction Throughput
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Solution Overview
Problem
Existing memory systems with multi-level cache hierarchies face inefficiencies in cache allocation and transaction processing due to cache coherence states and varying access speeds, leading to potential bottlenecks and reduced performance.
Innovation Solution
Implementing dynamic arbitration methods in the L2 cache subsystem, including random selection of cache ways, prioritization of transactions based on priority, and adaptive caching modes, along with mechanisms to manage cache coherence and transaction types to optimize allocation and processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cache lines are allocated using traditional arbitration methods in multi-level cache hierarchies, then cache coherence management becomes complex, but allocation efficiency and system throughput are reduced
Solution Approach 1:
The patent changes the arbitration parameter from complex coherence state checking to simple random selection among valid ways. Instead of evaluating multiple coherence conditions and making deterministic decisions, the system uses random selection as the arbitration parameter, fundamentally simplifying the allocation logic while maintaining cache coherence through the validity bit check.
Solution Approach 2:
The system allows the cache allocation process to serve itself through automated random selection among valid ways. The arbitration logic automatically identifies valid ways (those with invalid coherence state) and performs allocation without requiring complex external control or manual intervention in the coherence management process.
2Productivity
If traditional pipeline arbitration is used for memory transactions, then transaction processing follows fixed priority, but performance bottlenecks occur under varying workload conditions
Solution Approach 1:
The patent introduces dynamic arbitration into the memory pipeline by allowing priority assignments to change based on current system state and workload conditions. Instead of fixed priority queues, the arbitration mechanism adapts dynamically to select which transaction to process next, enabling the system to respond flexibly to varying workload patterns and prevent bottlenecks.
Solution Approach 2:
The arbitration system uses feedback from the current pipeline state and transaction characteristics to make intelligent routing decisions. The system monitors transaction types, pipeline occupancy, and coherence states, then feeds this information back into the arbitration logic to determine optimal transaction processing order, improving throughput under different workload conditions.
3Reliability
If deterministic cache way selection is used, then allocation is predictable, but random access patterns suffer from cache thrashing
Solution Approach 1:
The patent applies partial randomization only to the cache way selection among valid ways, rather than completely randomizing all allocations. This partial application of randomness maintains some predictability (by only affecting way selection among available options) while sufficiently disrupting patterns to reduce cache thrashing and improve hit rates for random access workloads.
Data Source
AI summary
A method includes receiving, by a first stage in a pipeline, a first transaction from a previous stage in pipeline; in response to first transaction comprising a high priority transaction, processing high priority transaction by sending high priority transaction to a buffer; receiving a second transaction from previous stage; in response to second transaction comprising a low priority transaction, processing low priority transaction by monitoring a full signal from buffer while sending low priority transaction to buffer; in response to full signal asserted and no high priority transaction being available from previous stage, pausing processing of low priority transaction; in response to full signal asserted and a high priority transaction being available from previous stage, stopping processing of low priority transaction and processing high priority transaction; and in response to full signal being de-asserted, processing low priority transaction by sending low priority transaction to buffer.