Compiler Optimizations for Reducing Transactional Abort Rates
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Solution Overview
Problem
Transactional memory systems experience performance degradation due to high abort rates caused by conflicts between concurrent threads, which are not effectively addressed by existing technologies.
Innovation Solution
A compiler performs optimizations such as store deferral, hoisting, speculative hoisting, redundant store squashing, and data layout optimizations to minimize store-commit intervals and reduce transactional aborts by analyzing and transforming the source or intermediate code representations to generate optimized output code that reduces conflict risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple threads execute concurrently in a transactional memory system, then system throughput and parallelism are improved, but transactional abort rates increase due to conflicts between threads
Solution Approach 1:
The compiler performs preliminary analysis of the transaction body to identify store operations and calculates their dependency chains before code generation. By pre-computing which stores must be included in the transaction and which can be hoisted or deferred, the system prepares an optimized execution plan that minimizes conflict exposure time while maintaining correctness, thereby reducing abort rates in concurrent environments
Solution Approach 2:
The invention extracts and removes redundant store operations from the transaction body that do not contribute to the transaction's computational outcome. By analyzing data dependencies and identifying stores that are overwritten or never read, the compiler eliminates unnecessary memory writes that would otherwise extend the store-commit interval and increase conflict probability with other threads
2Reliability
If the compiler performs comprehensive data dependency analysis and code transformations, then transactional abort rates are reduced, but compilation complexity and processing time increase
Solution Approach 1:
The compiler implementation is divided into distinct modular components: a data dependency analysis module that builds dependency graphs, a code transformation module that applies hoisting and deferral optimizations, and a redundant store elimination module. This segmentation allows each component to be independently optimized and maintained, reducing overall system complexity while enabling comprehensive analysis
Solution Approach 2:
The invention introduces an intermediate representation (IR) stage between source code parsing and final code generation. This IR serves as a mediator that explicitly represents data dependencies and control flow, making it easier for subsequent optimization passes to analyze and transform the code without requiring complex direct analysis of the source language semantics
3Ease of operation
If store operations are performed early in a transaction body, then program logic is simpler to implement, but the store-commit interval is lengthened increasing abort risk
Solution Approach 1:
Instead of performing store operations as early as possible in the transaction body, the compiler inverts the optimization strategy by deferring stores to occur as late as possible, immediately before the commit instruction. This inversion reduces the store-commit interval duration and minimizes the window for conflicts with other threads, while the compiler's dependency analysis ensures correctness is maintained
4Measurement precision
If long-latency calculations are performed inside a transaction, then computational accuracy is maintained, but the transaction duration is extended increasing conflict probability
Solution Approach 1:
The compiler identifies long-latency calculations within transaction bodies and hoists them to occur before the transaction begins or in separate non-critical sections. By performing these computations preliminarily and caching their results, the system maintains computational accuracy while significantly reducing the time the transaction holds locks and is vulnerable to conflicts
Solution Approach 2:
When hoisting long-latency calculations outside the transaction, the compiler creates copies of the calculation results and stores them in memory or registers. These copied values are then referenced within the transaction instead of re-computing them, preserving accuracy while minimizing transaction duration and abort risk
Data Source
AI summary
In transactional memory systems, transactional aborts due to conflicts between concurrent threads may cause system performance degradation. A compiler may attempt to minimize runtime abort rates by performing code transformations and/or other optimizations on a transactional memory program in an attempt to minimize store-commit intervals. The compiler may employ store deferral, hoisting of long-latency operations from within a transaction body and/or store-commit interval, speculative hoisting of long-latency operations, and/or redundant store squashing optimizations. The compiler may perform optimizing transformations on source code and/or on any intermediate representation thereof (e.g., parse trees, un-optimized assembly code, etc.). The compiler may preemptively avoid naïve target code constructions. The compiler may perform static and/or dynamic analysis of a program in order to determine which, if any, transformations should be applied and/or may dynamically recompile code sections at runtime, based on execution analysis.