Register File Checkpointing with Mapper-Based Dual-Slave Flops
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Solution Overview
Problem
In-order processors face inefficiencies in checkpointing, as they cannot reorder instruction execution, leading to performance bottlenecks during speculative processing and transactional memory operations, where capturing and restoring previous architectural states is time-consuming due to the need to copy large amounts of register data.
Innovation Solution
Implementing a single-master/dual-slave flop design for checkpointing, which allows efficient mapping of architectural registers to a larger set of physical registers, enabling fast checkpointing by transferring only mapping information, rather than register data, and using control circuitry to manage checkpoint capture and restoration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional checkpointing is used in in-order processors, then architectural states can be captured and restored, but performance overhead increases due to time-consuming data copying
Solution Approach 1:
The patent applies the copying principle by creating a mapping structure that maps architectural registers to physical registers. Instead of copying actual register data during checkpointing, the system copies only the mapping information (which physical register corresponds to which architectural register). This dramatically reduces the amount of data that needs to be copied while still enabling complete state restoration when needed.
Solution Approach 2:
The patent introduces a mapping structure as an intermediary between architectural registers and physical registers. This mapping structure acts as a mediator that enables checkpointing by storing only the mapping relationships rather than the actual register contents. The mapping structure allows the system to track which physical registers hold data for which architectural registers without copying the register data itself.
2Stability of the object's composition
If in-order processing is used, then instruction execution follows program order, but speculative processing and transactional memory operations become inefficient
Solution Approach 1:
The mapping structure enables efficient speculative processing by allowing fast copying of only mapping information rather than full register states. When speculative execution needs to commit or rollback, the system can quickly update or restore the mapping structure, enabling efficient transactional memory operations while maintaining in-order execution semantics.
Data Source
AI summary
Area-efficient logic circuitry for checkpointing a register file using a mapper in an “in-order” CPU (central processing unit). A pair of flops with a shared master stage latch circuit implement storage elements in a register file and a checkpointed copy of the same register file.