Prefetch Request Priority Management for Transactional Memory
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Solution Overview
Problem
Transactional memory systems face performance degradation due to prefetch instructions causing transactions to abort due to address conflicts, particularly when prefetch requests from remote processors have higher priority than ongoing transactions.
Innovation Solution
Implement a method to evaluate prefetch requests for potential conflicts with transactions by comparing priorities and delaying or quiescing prefetch requests to avoid aborting transactions, using a prefetch protocol that manages read and write operations to prevent transaction failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If prefetch requests are executed with high priority to improve data retrieval speed, then cache access efficiency is improved, but transaction aborts increase due to address conflicts
Solution Approach 1:
The patent applies preliminary action by evaluating prefetch requests before they are executed. The system performs a conflict detection check in advance to determine whether a prefetch request would cause a transaction abort, and only allows the prefetch to proceed if no conflict is predicted. This prevents the harmful effect before it occurs, resolving the contradiction between fast prefetch execution and transaction reliability.
2Reliability
If prefetch requests are delayed or quiesced to prevent transaction aborts, then transaction reliability is improved, but cache access efficiency decreases
Solution Approach 1:
The patent implements feedback by continuously monitoring the state of in-flight transactions and using this information to make dynamic decisions about prefetch request handling. The conflict detection mechanism provides feedback about potential address conflicts, and the system adjusts prefetch execution accordingly - allowing prefetches when safe and delaying/quiescing them when conflicts are predicted. This feedback loop resolves the contradiction by optimizing both reliability and speed based on real-time system state.
3Device complexity
If prefetch requests are allowed to execute without conflict detection, then system complexity is reduced, but transaction aborts increase
Solution Approach 1:
The patent introduces an intermediary conflict detection mechanism that sits between the prefetch request generator and the cache execution unit. This intermediary evaluates potential address conflicts by comparing prefetch addresses against active transaction addresses, and mediates the execution decision. While this adds some complexity, it provides a structured and manageable approach to preventing transaction aborts, resolving the contradiction between simplicity and reliability.
Data Source
AI summary
Modifying prefetch request processing. A prefetch request is received by a local computer from a remote computer. The local computer responds to a determination that execution of the prefetch request is predicted to cause an address conflict during an execution of a transaction of the local processor by comparing a priority of the prefetch request with a priority of the transaction. Based on a result of the comparison, the local computer modifies program instructions that govern execution of the program instructions included in the prefetch request to include program instruction to perform one or both of: (i) a quiesce of the prefetch request prior to execution of the prefetch request, and (ii) a delay in execution of the prefetch request for a predetermined delay period.