Cache-Coherent PPU Partitions With CPU Ownership Tracking
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Solution Overview
Problem
Conventional multiprocessor systems face challenges in maintaining memory coherency across multiple partitions, particularly in multitenant configurations, where the burden of avoiding conflicting memory accesses falls on software engineers, leading to increased complexity and potential operational errors.
Innovation Solution
Implementing techniques that allow CPU hardware to track and manage memory ownership and coherency by associating unique identifiers with each partition, enabling the CPU to grant and reclaim ownership of memory addresses, thus reducing the need for software applications to handle conflicts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If GPU partitions access CPU memory address space without hardware tracking, then device complexity is reduced, but memory coherency reliability deteriorates due to conflicting memory accesses
Solution Approach 1:
The patent introduces a hardware tracking mechanism that acts as an intermediary between GPU partitions and CPU memory. This mechanism monitors and manages memory access requests from multiple GPU partitions, ensuring that only the owning partition can access a given CPU memory address at any time. The hardware tracker resolves conflicts before they reach the memory system, maintaining coherency without requiring complex software management.
Solution Approach 2:
The system implements feedback through hardware tracking of memory ownership and access patterns. When a GPU partition attempts to access CPU memory, the hardware tracker provides feedback about current ownership status. If the accessing partition is not the owner, the hardware generates a conflict signal that prevents the access or triggers an ownership transfer protocol, ensuring coherency through continuous monitoring and response.
2Device complexity
If software applications are responsible for avoiding conflicting memory accesses, then hardware complexity is reduced, but ease of operation deteriorates due to increased software design burden
Solution Approach 1:
The hardware tracking mechanism provides self-service by automatically managing memory ownership and detecting conflicts without software intervention. The system autonomously tracks which GPU partition owns each CPU memory address and prevents conflicting accesses at the hardware level. This eliminates the need for software engineers to implement complex conflict avoidance logic, allowing applications to access memory using simple, standard operations.
3Manufacturing precision
If GPU partitions have separate GPU memory address spaces, then manufacturing precision is improved through dedicated address mapping, but adaptability deteriorates as CPU cannot dynamically allocate memory across partitions
Solution Approach 1:
The hardware tracking mechanism provides multi-functionality by serving both the precision requirements of separate address spaces and the flexibility needs of dynamic allocation. It maintains distinct GPU memory address spaces for each partition while simultaneously enabling the CPU to dynamically allocate and manage CPU memory addresses across multiple partitions. The tracker adapts to different allocation scenarios without requiring changes to the fundamental address space structure.
Data Source
AI summary
Various embodiments include techniques for processing memory operations in a computing system. The computing system includes a central processing unit (CPU) and an auxiliary processor, such as a parallel processing unit (PPU). The PPU can be divided into multiple partitions. Although the partitions are included in a single PPU, the CPU can track the partitions as if the partitions are independent devices rather than different portions of a single device. When two different partitions generate memory operations that access the same memory address in CPU memory address space, the two partitions employ two different data paths. The CPU can use path information for the two different paths to identify which partition generated each memory operation. As a result, the CPU can maintain data consistency and memory coherency in a system where a PPU is divided into multiple partitions.