Page Table Entry Cache with Variable Tag Lengths for IOMMU Translation
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Solution Overview
Problem
Current address translation systems in IOMMUs face inefficiencies in handling multi-stage address translations for virtual machines, leading to increased cache sizes and reduced performance due to the lack of effective tagging mechanisms for privilege levels, virtualization modes, and translation modes.
Innovation Solution
Implementing an address translation engine with a page table entry cache that uses translation tags indicating privilege levels, virtualization modes, and translation modes to efficiently manage and accelerate address translations by differentiating between various translation types and optimizing cache usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional MMU handles multi-stage address translations for virtual machines, then address translation functionality is provided, but cache size increases and performance decreases due to lack of effective tagging mechanisms
Solution Approach 1:
The patent segments the address translation cache into multiple subsets, where each subset handles a specific stage of address translation (e.g., first-stage and second-stage translations). This segmentation allows the cache to manage different translation types separately, reducing the overall cache size needed while maintaining support for multi-stage translations for virtual machines.
Solution Approach 2:
The patent applies different tagging mechanisms to different subsets of the cache based on their specific functions. Each subset uses customized tag fields tailored to its translation stage requirements, optimizing the cache structure for local needs rather than using a uniform approach throughout the entire cache.
2Adaptability or versatility
If a traditional MMU handles multi-stage address translations, then translation functionality is provided, but translation speed decreases due to lack of effective tagging mechanisms
Solution Approach 1:
By dividing the translation cache into multiple subsets for different translation stages, the patent enables parallel processing of translation operations. Each subset can independently handle its specific stage without blocking others, thereby increasing overall translation throughput and speed while maintaining multi-stage translation capability.
Solution Approach 2:
The patent optimizes each cache subset with locally-appropriate tagging mechanisms that are specifically designed for its translation stage. This localized optimization reduces tag comparison time and improves hit rates for each stage, thereby accelerating the overall translation process.
3Reliability
If cache size is increased to handle all translation types, then translation completeness is improved, but address translation performance decreases
Solution Approach 1:
The patent segments the cache into multiple specialized subsets, each handling a specific translation stage or type. This allows the system to maintain comprehensive translation coverage (reliability) while keeping each individual cache subset smaller and faster, thereby improving overall translation performance (productivity).
Solution Approach 2:
Each cache subset is optimized with locally-appropriate parameters and tagging mechanisms tailored to its specific function. This localized optimization ensures that each subset operates at high speed for its designated translation tasks while collectively providing complete translation support across all stages.
Data Source
AI summary
Systems and methods are disclosed for page table entry caches with multiple tag lengths. For example, an integrated circuit (e.g., a processor) includes a page table walk circuitry including a page table entry cache, in which the page table walk circuitry is configured to access a multi-level page table, and in which a first entry of the page table entry cache combines a first number of multiple levels and a second entry of the page table entry cache combines a second number of multiple levels that is different from the first number of multiple levels.