Task Descriptor Prefetching for Parallel Processing Latency
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Solution Overview
Problem
In parallel processing systems, the dependency resolution latency between producer and consumer tasks in task graphs is high, leading to increased overall execution time, particularly for workloads with short execution times, due to factors like data storage and retrieval from memory.
Innovation Solution
Implementing a method that includes determining task dependencies, initiating a task descriptor retrieval from memory before the producer task's execution, and launching the consumer task based on the retrieved descriptor after the producer task's execution, while also enabling prefetching of task descriptors, instructions, and constants in parallel with producer task activities, and automatically re-initializing dependency tracking without software intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If task descriptors are retrieved from memory after producer task completion, then data dependency is ensured, but dependency resolution latency increases
Solution Approach 1:
The system performs preliminary actions by initiating the retrieval of task descriptors for consumer tasks before the producer task actually completes. The PPU hardware automatically starts fetching task descriptors from memory during the producer task execution, so that when the producer completes, the consumer task descriptor is already available in the task management unit, eliminating the wait time.
Solution Approach 2:
The patent introduces an intermediary mechanism - a task management unit with a task descriptor cache - that sits between memory and the task execution pipeline. This intermediary pre-loads and stores task descriptors, acting as a buffer that decouples the memory retrieval time from the task execution timing, thereby reducing the critical path latency.
2Reliability
If all threads executing a task must complete before consumer tasks begin, then execution dependency is ensured, but overall execution time increases
Solution Approach 1:
The system performs preliminary preparation of consumer tasks by having their descriptors retrieved and staged in advance during the producer task execution. This preliminary action allows the consumer task to start immediately upon producer completion without additional delay, maintaining execution dependency while minimizing idle time.
Solution Approach 2:
The patent enables continuity of useful action by overlapping the execution of producer tasks with the preliminary setup of consumer tasks. While producer threads are executing, the system continuously prepares consumer task descriptors in parallel, ensuring that no time is wasted in the transition between tasks, thus maintaining continuous productive work.
3Quantity of substance
If task descriptors are stored in memory, then data storage is achieved, but retrieval time contributes to latency
Solution Approach 1:
The system extracts the task descriptor data from main memory and places it into a dedicated task management unit with a task descriptor cache. This extraction moves frequently accessed task descriptors out of the slower main memory into a faster, specialized storage location within the PPU, reducing retrieval time while maintaining data availability.
Solution Approach 2:
The patent creates copies of task descriptors by maintaining them in both memory and in the task management unit's cache. The preliminary retrieval action creates a local copy that can be accessed quickly during task execution, eliminating the need to repeatedly access main memory for the same descriptor data.
4Measurement precision
If dependency tracking requires software intervention, then accuracy is maintained, but system complexity increases
Solution Approach 1:
The system implements self-service by enabling the PPU hardware to automatically track and manage task dependencies without requiring software intervention. The task management unit autonomously monitors producer task completion, manages consumer task descriptor retrieval, and coordinates execution timing, thereby maintaining accurate dependency tracking while eliminating the need for complex software dependency management routines.
Data Source
AI summary
Techniques are disclosed for reducing the latency between the completion of a producer task and the launch of a consumer task dependent on the producer task. Such latency exists when the information needed to launch the consumer task is unavailable when the producer task completes. Thus, various techniques are disclosed, where a task management unit initiates the retrieval of the information needed to launch the consumer task from memory in parallel with the producer task being launched. Because the retrieval of such information is initiated in parallel with the launch of the producer task, the information is often available when the producer task completes, thus allowing for the consumer task to be launched without delay. The disclosed techniques, therefore, enable the latency between completing the producer task and launching the consumer task to be reduced.