Load-Checking Atomic Section for Shared Memory Concurrency
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Solution Overview
Problem
In shared-memory multiprocessor architectures, out-of-order execution of instructions can lead to data races and incorrect results due to concurrent modifications of shared memory locations, which existing technologies struggle to prevent or correct effectively, especially when speculative execution is involved.
Innovation Solution
The compiler transforms programs by speculatively advancing 'load' instructions out of atomic sections and adding check instructions within these sections to ensure that stores and checks remain within atomic sections, allowing for concurrent execution while maintaining logical order and preventing data races.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If out-of-order execution is used to improve performance, then execution speed increases, but data race errors and incorrect results occur
Solution Approach 1:
The patent applies preliminary action by executing load instructions before their logical order position (speculative execution) and using check instructions to validate results later. The advanced-load address table pre-tracks addresses accessed by advanced loads, enabling early execution while maintaining correctness through subsequent validation.
Solution Approach 2:
The patent implements feedback through check instructions that validate the results of advanced load instructions. If a check instruction detects that a memory location was modified between the advanced load and its logical position, the system corrects the error by reloading the correct value, thus providing feedback to ensure data correctness.
2Reliability
If atomic sections are used to prevent data races, then data correctness is ensured, but lock contention and performance degradation occur
Solution Approach 1:
The patent extracts load instructions from atomic sections by allowing them to execute outside the atomic boundary using advanced load instructions. Only the critical store operations remain within atomic sections, reducing the scope of mutual exclusion and minimizing lock contention while maintaining data correctness through check instructions.
Solution Approach 2:
The patent segments the atomic section into two parts: advanced load instructions that execute outside the atomic section for performance, and check instructions that validate within the atomic section for correctness. This segmentation allows concurrent execution without sacrificing data race prevention.
3Speed
If load instructions are advanced out of atomic sections to improve performance, then execution speed increases, but load validation complexity increases
Solution Approach 1:
The patent introduces an advanced-load address table as an intermediary structure to track addresses accessed by advanced load instructions. This table mediates between the speculative execution mechanism and the validation mechanism, storing address information that enables check instructions to efficiently validate loads without complex validation logic.
Data Source
AI summary
A compiled program has an advanced-load instruction and a load-checking atomic section. The load-checking atomic section follows the advanced-load instruction in the compiled program. The advanced-load instruction, when executed, loads a value from a shared memory address. The load-checking atomic section includes a check instruction for checking the validity of the shared memory address.