Hardware-Assisted Page Migration in Multi-Dielet Systems
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Solution Overview
Problem
In multi-dielet processing systems, coordinating page migration operations between different chip modules is challenging, leading to inefficiencies and increased latency in accessing memory, particularly in systems with multiple dielets where each GPU chip module requires independent management of access counter modules and notify buffers.
Innovation Solution
Implementing a unified view of page migration by ensuring each access counter module across dielets is informed of memory bindings and accesses across all dielets, using mechanisms like MMU broadcasts and inter-dielet communication to synchronize bind information and maintain accurate notifications for on-demand page migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If each dielet manages its own access counter modules and notify buffers independently, then device complexity is reduced and ease of manufacture is improved, but coordination efficiency deteriorates and latency increases
Solution Approach 1:
The patent introduces a chief access counter module as an intermediary that coordinates page migration operations across multiple dielets. This chief module receives notifications from other dielets and manages the centralized notify buffer, enabling efficient inter-dielet communication without requiring each dielet to independently manage all coordination aspects. This resolves the contradiction by maintaining independent dielet management structure while adding a mediation layer for efficient coordination.
Solution Approach 2:
The patent segments the access counter functionality into local access counter modules on each dielet and a chief access counter module that coordinates across dielets. This segmentation allows each dielet to maintain independent local management while the chief module provides centralized coordination for page migration notifications. The segmentation enables parallel operation of local counters while reducing coordination overhead through the chief module's centralized management.
2Device complexity
If access counter modules are distributed across multiple dielets, then device complexity is reduced, but information synchronization becomes more difficult and measurement precision deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where access counter modules on different dielets send notifications to a centralized notify buffer managed by the chief access counter module. This feedback loop ensures that bind information is synchronized across all dielets, as each dielet's access patterns are communicated to the chief module which then coordinates appropriate page migration actions. This resolves the information synchronization issue while maintaining distributed architecture.
Solution Approach 2:
The patent merges the notify buffer resources into a centralized structure managed by the chief access counter module, while keeping the access counter modules distributed across dielets. This merging of the notification infrastructure ensures that all dielets have access to consistent bind information through the shared notify buffer, eliminating information loss while preserving the benefits of distributed counter modules.
3Productivity
If on-demand page migration is implemented, then memory access efficiency is improved, but device complexity increases due to coordination requirements
Solution Approach 1:
The patent enables on-demand page migration where the system automatically migrates pages based on actual access patterns detected by the access counter modules. Instead of requiring complex pre-coordination of all possible page migrations, the system allows each dielet to independently monitor its own access patterns and trigger migrations only when needed. The chief access counter module coordinates these on-demand migrations efficiently, reducing overall complexity while maintaining high memory access efficiency.
Data Source
AI summary
A hardware mechanism at each dielet of a multi-dielet processing system is aware of engine page-table binds at all the dielets, thereby providing accurate traffic notifications to software (e.g., a unified virtual memory driver) for on-demand page-migration between system memory and GPU memory. The mechanism broadcasts binding information to access counters on each dielet so the access counters are able to correlate engines requesting memory access with bound virtual memory pages and generate corresponding informative notifications. A flexible multi-dielet counter clear capability enables software to clear access counters.