Load Replay Prediction for Rescheduling Costly Processor Instructions
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Solution Overview
Problem
Execution of load instructions on a processor device is costly due to data movement and often requires re-execution (replay), leading to performance reduction.
Innovation Solution
Maintain load replay data to determine if a load instruction has been previously replayed, and reschedule it if necessary to avoid subsequent costly replays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If load instructions are executed by the load store unit, then data is loaded from memory to register, but the operation is costly and may require re-execution (replay)
Solution Approach 1:
The patent applies preliminary action by predicting whether a load instruction will need to be replayed before actually executing it. The load replay predictor checks historical replay data in advance, and if a replay is likely, the instruction is rescheduled to a different execution time. This prevents the costly replay operation from occurring in the first place, thereby maintaining correctness while improving processor performance by avoiding redundant executions.
2Productivity
If load instructions are rescheduled based on past replay data, then subsequent replays are avoided, but additional prediction and data access operations are introduced
Solution Approach 1:
The patent uses copying by maintaining a replay history data structure that stores information about previous load instruction replays. Instead of modifying the core execution pipeline, the system creates a separate copy of replay information that can be queried by the load replay predictor. This allows the predictor to access historical data without interfering with the normal load execution path, thereby improving performance while adding minimal complexity.
Data Source
AI summary
Rescheduling a load instruction based on past replays is disclosed. A load replay predictor of a processor device determines, at a first time, that a load instruction is scheduled to be executed by a load store unit to load data from a memory location. The load replay predictor accesses load replay data associated with a previous replay of the load instruction and, based on the load replay data, causes the load instruction to be rescheduled.