Distributed Page Table Management for CPU-GPU Memory Coherency
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Solution Overview
Problem
Current systems face performance overhead due to CPU-handled GPU page faults, which cause contention and memory corruption risks, hindering efficient page table management and memory coherency across CPUs and GPUs.
Innovation Solution
Implementing a distributed page table management system where both CPU and GPU can independently handle page faults, reducing reliance on CPU intervention and optimizing page table updates through parallel processing units and unified memory architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CPU handles all GPU page faults to prevent page table contention and memory corruption, then system reliability is improved, but performance overhead increases significantly
Solution Approach 1:
The patent segments page fault handling authority between CPU and GPU by introducing separate page table structures (CPU page tables and GPU page tables) and distinct handling mechanisms. The GPU can independently handle its own page faults through GPU page tables and TLB, while CPU maintains authority for unified memory management, thus distributing the workload and improving performance while maintaining reliability through controlled segmentation.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of a unified memory architecture with coordinated page table management. The IOMMU and unified page tables act as intermediaries that allow GPU autonomous page fault handling while maintaining CPU oversight and global memory coherence, thus resolving the contradiction between autonomous handling and centralized control.
2Reliability
If single entity (CPU) manages page fault handling to prevent page table read/write contention, then memory corruption risk is reduced, but CPU and GPU performance suffer from overhead
Solution Approach 1:
The patent divides page table management into separate CPU page tables and GPU page tables, allowing parallel access and independent management. This segmentation eliminates read/write contention by providing dedicated page table structures for each processor type, thus preventing memory corruption while reducing page fault resolution time through parallel processing.
Solution Approach 2:
The patent enables the GPU to serve itself by implementing autonomous page fault handling capability. The GPU can independently manage its own page faults using GPU page tables and TLB without requiring CPU intervention for every page fault, thus reducing CPU overhead and page fault resolution time while maintaining memory integrity through coordinated management.
3Reliability
If unified memory architecture is implemented to improve memory coherency, then memory management efficiency is enhanced, but complex page table coordination is required
Solution Approach 1:
The patent implements a universal page table management system where unified memory architecture allows both CPU and GPU to access the same memory space through coordinated page tables. The IOMMU serves multiple functions by managing both CPU and GPU address translations, thus improving memory coherency while handling complexity through a multi-functional unified management approach.
Data Source
AI summary
An apparatus and method for page table management. For example, one embodiment of an apparatus comprises: a memory management circuit to perform address translations using a page directory, a base page directory address identifying a location of the page directory in a system memory; a cache to reserve a first cache line containing the base page directory address stored in a modified state; cache snoop circuitry to detect a read to the base page directory address by a processor or graphics processing unit (GPU); and locking circuitry to assert a lock signal to change the state of the first cache line to a locked state, the memory management circuit to refrain from performing a page table walk until the lock signal is de-asserted.