Vector Processor Conditional Dependency Resolution
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Solution Overview
Problem
Existing parallel-processing systems face impediments in vectorizing or parallelizing computational operations due to structural hazards caused by conditional data dependencies, which are unpredictable and lead to conservative compilation approaches, preventing effective parallel or vector processing.
Innovation Solution
A method and system that allow parallel operations in the presence of conditional dependencies by generating stop indicators and predicate values based on tracked positions of actual dependencies, enabling processors to determine when data elements can be safely processed in parallel or sequentially, thereby mitigating structural hazards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compiler takes the conservative approach and does not vectorize in the presence of a possible loop-carried dependency, then program correctness is maintained, but parallel processing performance is degraded
Solution Approach 1:
The patent segments the vector processing into multiple passes: a first pass that identifies potential structural hazards and generates stop indicators, and subsequent passes that can safely execute parallel operations. This segmentation allows the system to maintain correctness while enabling parallelization by dividing the processing into hazard-detection and hazard-execution phases.
Solution Approach 2:
The patent performs preliminary analysis during compilation to identify potential structural hazards and generate stop indicators before actual execution. This preliminary action allows the runtime system to know in advance where dependencies may occur, enabling it to safely parallelize operations while maintaining correctness by placing stop indicators at appropriate locations.
2Reliability
If the compiler assumes loops with loop-carried dependencies cannot be vectorized, then correctness is maintained, but the degree of parallelization is reduced
Solution Approach 1:
The patent introduces dynamic stop indicators that are generated at runtime based on actual condition variable states rather than static compiler assumptions. This dynamic approach allows the system to adaptively determine where parallelization is safe, increasing the degree of parallelization while maintaining correctness by placing stop indicators only where actual dependencies exist.
Solution Approach 2:
The patent changes the parameter of dependency detection from static (compiler-time) to dynamic (runtime), allowing the system to recognize that loop-carried dependencies may not always be present. By evaluating condition variables at runtime, the system can vectorize loops that would traditionally be assumed to have dependencies, thereby increasing parallelization capability while maintaining correctness.
3Reliability
If structural hazards are prevented through conservative compilation, then parallel processing safety is ensured, but processing efficiency is reduced
Solution Approach 1:
The patent introduces stop indicators as intermediary markers that mediate between hazard prevention and performance optimization. These stop indicators are inserted at strategic locations in the vector code and allow the processing system to safely parallelize operations while maintaining correctness by stopping at appropriate points to check for actual dependencies, thus reducing unnecessary conservative restrictions.
Solution Approach 2:
The patent implements a feedback mechanism where stop indicators provide information about actual dependency states during execution. This feedback allows the system to adjust its parallelization strategy dynamically, enabling efficient parallel processing in regions where dependencies are absent while maintaining safety by stopping in regions where dependencies are detected, thereby reducing overall processing time compared to conservative approaches.
Data Source
AI summary
Described is a method for performing parallel operations in a computer system when one or more conditional dependencies may be present, where a given conditional dependency includes a dependency associated with at least two data elements based on a pair of conditions. During operation, a processor receives instructions for generating a vector of tracked positions of actual dependencies, where a given tracked position indicates the position of a given actual dependency, and where the given actual dependency occurs when the pair of condition matches one or more criteria. Then, the processor executes the instructions for generating the vector of tracked positions.