Remote Address Translator Cache for DMA Latency
Solution Overview
Problem
Current DMA systems face inefficiencies in address translation due to inadequate latency management and unnecessary invalidation protocols, particularly when devices have varying access patterns and cache invalidation strategies, leading to increased latency and resource misuse.
Innovation Solution
Implementing a remote address translator (RAT) with a cache that distinguishes between priority and non-priority translations, allowing selective caching and invalidation based on usage patterns, and notifying only priority translations of changes to prevent data errors and reduce unnecessary invalidations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a centralized IOTLB is used to cache address translations for multiple DMA devices, then memory management is simplified and centralized control is improved, but access latency increases due to distance and contention
Solution Approach 1:
The patent segments the centralized IOTLB into device-specific IOTLB instances, with each DMA device having its own dedicated cache. This segmentation reduces access latency by eliminating contention between devices while maintaining simplified management through centralized coordination of invalidation protocols.
Solution Approach 2:
The patent introduces a translation service as an intermediary component that coordinates between the centralized address translation authority and device-specific IOTLB instances. This intermediary manages the invalidation protocols and ensures consistency across the distributed cache structure.
2Speed
If all address translations are cached in the IOTLB, then access speed is improved, but cache invalidation overhead increases when address mappings change
Solution Approach 1:
The patent implements selective caching where only frequently accessed or critical address translations are maintained in the IOTLB, rather than caching all translations. This partial caching approach maintains high access speed for important operations while reducing the overhead of invalidating the entire cache when mappings change.
Solution Approach 2:
The patent implements dynamic cache management where the IOTLB selectively retains or invalidates entries based on usage patterns and change detection. The cache adapts its content dynamically, keeping valid entries for speed while discarding stale entries to minimize invalidation overhead.
3Loss of time
If device-specific IOTLB instances are implemented for each DMA device, then access latency is reduced through local caching, but system complexity and resource requirements increase
Solution Approach 1:
The patent implements a universal IOTLB design where a single cache structure serves multiple DMA devices through the translation service intermediary. This multi-functional approach provides device-specific caching benefits without requiring separate physical IOTLB instances for each device, thus reducing system complexity while maintaining low latency.
4Speed
If the IOTLB caches translations proactively, then future access speed is improved, but memory resources are consumed by cached entries that may become invalid
Solution Approach 1:
The patent implements feedback mechanisms where the translation service monitors address mapping changes and provides invalidation notifications to the IOTLB. This feedback loop ensures that cached translations remain valid by systematically updating or invalidating entries when source addresses are remapped, maintaining both speed and reliability.
Data Source
AI summary
A computing system has a resource for providing resource services, where each resource service is accessed by way of a system address (SA). A device requests the resource services of the resource by way of requests, where each request includes a remote address (RA) corresponding to an SA of the resource. A centralized address translator (CAT) has a database of RA/SA translations for the resource and the device, where each RA/SA translation in the database corresponds to a respective RA and SA. The device has a remote address translator (RAT) with a cache for storing priority RA/SA translations as obtained from the CAT. Each priority RA/SA translation in the cache of the RAT includes a validity flag set to indicate whether the priority translation is valid based on whether the SA has changed at the CAT.