Long Transaction Execution via Deferred Store Commit
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Solution Overview
Problem
Existing synchronization mechanisms, such as mutual-exclusion locking, can lead to deadlocks, excessive latency, and priority inversion in systems with limited transactional hardware resources, making it challenging to execute long transactions efficiently.
Innovation Solution
A system that executes long transactions in a non-transactional mode, deferring stores to a thread-specific commit buffer and committing them using multiple hardware transactions or multi-word compare and swap operations, allowing for lock-free execution and parallelism without relying on transactional hardware resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hardware transactional memory is used to execute transactions, then lock-freedom and increased parallelism are achieved, but the system is limited by finite transactional hardware resources and cannot support large transactions
Solution Approach 1:
The patent segments a long transaction into multiple short hardware transactions. Each short transaction processes a subset of the deferred stores within the hardware transaction resource limits. The system divides the workload across multiple transactions that are orchestrated to achieve the overall effect of the long transaction, thereby supporting large-scale operations within constrained hardware resources.
Solution Approach 2:
The system performs preliminary actions by deferring stores during the execution of the long transaction body without immediately committing them to the architectural state. This allows the transaction to accumulate all necessary store operations first, then commit them atomically at the end using multiple short hardware transactions, enabling long transactions to exceed individual hardware transaction limits.
2Reliability
If mutual-exclusion locking is used to protect critical sections, then atomicity is ensured, but deadlocks, excessive latency, and priority inversion occur
Solution Approach 1:
The patent replaces the mechanical mutual-exclusion locking mechanism with a software transactional memory approach using deferred stores and atomic commit operations. Instead of using locks that require thread blocking and potential deadlocks, the system uses a lock-free deferred store mechanism where multiple threads can execute concurrently and commit their stores atomically at the end, eliminating lock acquisition latency and deadlock risks while maintaining atomicity.
3Reliability
If a thread is stalled or preempted while executing a critical section under mutual exclusion, then other threads are blocked, but this causes excessive latency and priority inversion
Solution Approach 1:
The patent introduces deferred stores as an intermediary mechanism between thread execution and memory commitment. Instead of directly committing stores to memory during critical section execution (which blocks other threads), the system buffers stores in a deferred store structure and commits them atomically at the end. This intermediary allows concurrent thread execution without blocking, improving throughput while maintaining critical section protection through the atomic commit operation.
Data Source
AI summary
A system that executes a long transaction in a system with limited transactional hardware resources. During operation, the system executes the long transaction in a non transactional mode, which does not use transactional hardware resources. The system defers stores generated during the long transaction so that the stores are not committed to the architectural state of a processor until the transaction is successfully completed. If the long transaction successfully completes, the system commits the long transaction, which involves performing multiple hardware transactions to commit the deferred stores to the architectural state of the processor.