Livelock Resolution Circuit for Processor Reorder Buffer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Livelocks in processors occur when operations repeatedly interact without making progress, causing normal operations to halt, and existing techniques lack effective methods for detection and removal.
Innovation Solution
A livelock resolution circuit is implemented within a processor, utilizing a reorder buffer circuit and a decision circuit with a counter to detect livelocks by tracking operation retirement and generating signals to pause and single-step execute operations, thereby removing the livelock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If operations are allowed to execute continuously without intervention, then processor productivity is maintained, but livelock conditions cause operations to replay in infinite loops without making real progress
Solution Approach 1:
The reorder buffer circuit provides feedback by monitoring the retirement status of operations and detecting when operations fail to retire despite multiple execution attempts. This feedback mechanism identifies livelock conditions by tracking whether the oldest non-retired operation has been executed a predetermined number of times without retiring, enabling the system to intervene when normal execution patterns break down.
Solution Approach 2:
The livelock resolution circuit acts as an intermediary between the normal execution pipeline and the problematic operations. When a livelock is detected, this intermediary component takes control by pausing the execution pipeline and forcing single-step execution of the oldest non-retired operation, thereby breaking the infinite replay cycle and restoring reliable operation execution.
2Device complexity
If the execution pipeline continues operating during livelock conditions, then device complexity is minimized, but the livelock halts normal processor operations
Solution Approach 1:
The reorder buffer circuit performs multiple functions: it manages out-of-order execution, tracks operation retirement status, and detects livelock conditions. By making this existing component multi-functional, the patent avoids adding separate dedicated livelock detection hardware, thereby minimizing device complexity while still enabling effective livelock identification and resolution.
Solution Approach 2:
The system uses its own existing infrastructure—the reorder buffer and operation tracking mechanisms—to detect and resolve livelocks without requiring external intervention or complex additional hardware. The livelock resolution circuit leverages information already being collected for normal execution management, allowing the processor to self-diagnose and self-correct livelock conditions.
3Reliability
If operations are paused and executed in single-step mode, then livelock is resolved by forcing progress, but execution time increases due to pausing the execution pipeline
Solution Approach 1:
Instead of pausing the entire execution pipeline indefinitely or requiring full rollback of operations, the system applies partial action by targeting only the specific oldest non-retired operation suspected of causing the livelock. This focused intervention forces progress on the problematic operation while minimizing disruption to the overall execution flow, thereby reducing time loss compared to more aggressive pause-and-replay approaches.
Data Source
AI summary
A livelock resolution circuit may be used to detect and remove a livelock from a processor. The livelock resolution circuit may use a counter, whose value may be reset or incremented depending on a status of a retire pointer in a reorder buffer circuit (ROB). When the retire pointer fails to move from one operation to another over a period of time, the value in the counter may continuously increment to exceed a threshold, indicating that the period of time elapses without a successful retirement of an operation from the ROB. Thus, the livelock resolution circuit may determine that a livelock occurs. To remove the livelock, the livelock resolution circuit may involve a single-step operational mode, where the livelock resolution circuit may demand only one operation (or microoperation) to be executed at each step. As a result, the operation may be retired and the livelock may be removed.