Coalescing N-Way Memory Barrier Operations for Parallel Throughput
Solution Overview
Problem
In parallel processing architectures, executing memory barrier instructions across multiple threads is costly due to long latency, reducing instruction processing throughput, especially in systems with many threads and processors cooperating at multiple levels.
Innovation Solution
The method involves coalescing memory barrier operations by constructing a tagged memory command stream with a coalescing index for multiple thread groups, allowing simultaneous processing of memory transactions and barrier instructions, thereby reducing the impact on the system and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If memory barrier instructions are executed to ensure proper ordering and visibility of memory transactions across multiple threads, then memory transaction ordering and visibility are guaranteed, but instruction processing throughput is reduced due to long round-trip latency to the system memory commit point
Solution Approach 1:
The patent merges multiple memory barrier operations from multiple thread groups into a single coalesced memory barrier operation. The memory management unit combines barrier requests from N different thread groups, allowing them to be processed together in one system memory commit point round-trip, thereby reducing the frequency of throughput-reducing barrier executions while maintaining the required memory ordering and visibility guarantees.
Solution Approach 2:
The patent uses coalescing indices to create logical copies or groupings of memory transactions from different thread groups. By tagging transactions with coalescing indices and grouping them into bundles, the system can process multiple thread group barriers simultaneously without executing separate barrier instructions for each thread group, thus improving throughput while preserving reliability.
2Reliability
If memory barrier instructions are executed frequently to synchronize communication among thousands of parallel threads, then thread synchronization and communication correctness are ensured, but system performance deteriorates due to threads being idle during long-latency barrier execution
Solution Approach 1:
The patent combines memory barrier operations from multiple thread groups into coalesced operations at the memory management unit. By grouping barrier requests from N thread groups and processing them together, the system reduces the total number of barrier executions required, allowing threads to remain productive longer while still achieving the necessary synchronization and communication correctness through the coalesced barriers.
3Reliability
If separate memory barrier operations are executed for each thread group in a multi-threaded parallel system, then each thread group's memory ordering requirements are satisfied, but the overall system efficiency is reduced due to repeated long-latency operations
Solution Approach 1:
The patent merges separate memory barrier operations from multiple thread groups into coalesced operations. The memory management unit receives barrier requests from N different thread groups, combines them into a single coalesced operation, and processes them together at the system memory commit point. This approach satisfies the memory ordering requirements of all thread groups while significantly improving system efficiency by eliminating repeated long-latency round-trips.
Solution Approach 2:
The coalesced memory barrier operation serves multiple thread groups simultaneously, making a single barrier operation universal for N different thread groups. This multi-functional approach allows the system to maintain memory ordering for all thread groups through one unified barrier execution rather than requiring separate barrier operations for each group, thereby improving overall system efficiency.
Data Source
AI summary
One embodiment sets forth a technique for N-way memory barrier operation coalescing. When a first memory barrier is received for a first thread group execution of subsequent memory operations for the first thread group are suspended until the first memory barrier is executed. Subsequent memory barriers for different thread groups may be coalesced with the first memory barrier to produce a coalesced memory barrier that represents memory barrier operations for multiple thread groups. When the coalesced memory barrier is being processed, execution of subsequent memory operations for the different thread groups is also suspended. However, memory operations for other thread groups that are not affected by the coalesced memory barrier may be executed.