Compiler Region Scheduling for SIMD Thread Re-convergence
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Solution Overview
Problem
Existing techniques for managing thread execution in SIMD processors with divergent control flow paths are inefficient, leading to prolonged execution times and lack of early re-convergence in warps.
Innovation Solution
A compiler-controlled method that analyzes a control flow graph to assign execution priorities to regions, inserts update predicate mask variable instructions, and conditional branch instructions to schedule threads effectively, ensuring early re-convergence and efficient execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If threads execute all control flow paths in SIMD processors, then all threads can be processed, but execution time is prolonged due to thread divergence
Solution Approach 1:
The compiler performs preliminary analysis of the control flow graph to identify thread frontier regions and determine execution priorities before runtime execution. This allows the system to pre-establish the optimal execution order of regions, avoiding runtime decisions that would cause thread divergence and execution delays
Solution Approach 2:
The program is divided into multiple regions with assigned execution priorities. Threads are scheduled to execute regions in a prioritized sequence rather than following all control flow paths simultaneously. This segmentation allows the compiler to manage thread execution more efficiently by grouping threads that follow the same priority-based path
2Reliability
If existing thread scheduling techniques are used, then threads can execute, but re-convergence of threads is delayed
Solution Approach 1:
The system uses predicate mask variables that are updated at the end of each region to track which threads have completed which regions. This feedback mechanism allows the compiler to determine when all threads have reached a common point (re-convergence) and can schedule subsequent regions accordingly, ensuring early re-convergence while maintaining execution correctness
Data Source
AI summary
A compiler-controlled technique for scheduling threads to execute different regions of a program. A compiler analyzes program code to determine a control flow graph for the program code. The control flow graph contains regions and directed edges between regions. The regions have associated execution priorities. The directed edges indicate the direction of program control flow. Each region has a thread frontier which contains one or more regions. The compiler inserts one or more update predicate mask variable instructions at the end of a region. The compiler also inserts one or more conditional branch instructions at the end of the region. The conditional branch instructions are arranged in order of execution priority of the regions in the thread frontier of the region, to enforce execution priority of the regions at runtime.