TLB Compression via Hierarchical CAM Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern computing systems face performance issues due to frequent page table lookups caused by fragmented physical memory, which are exacerbated by the need for large translation lookaside buffers (TLBs) to handle virtual-to-physical address translations, leading to increased processing cycles and resource inefficiencies.
Innovation Solution
The implementation of a content addressable memory (CAM) that compresses Virtual Machine Identifiers (VMID) and Address Space Identifiers (ASID) associated with virtual addresses, reducing the size of the TLB and allowing for more efficient mapping of virtual addresses to physical addresses by storing compressed context data, thereby freeing up physical space on processing chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If large translation lookaside buffers (TLBs) are used to handle virtual-to-physical address translations, then address translation capability is improved, but chip area and resource utilization deteriorate
Solution Approach 1:
The patent segments the identifier into multiple parts and stores them in different locations within the CAM. Some parts are stored in high-order locations while others are stored in low-order locations, allowing the TLB to be divided into multiple smaller segments that can be searched in parallel, thereby reducing the overall TLB area while maintaining translation capability
Solution Approach 2:
The patent implements a hierarchical CAM structure where multiple CAMs are organized in a tree-like hierarchy. Each CAM contains a subset of the identifier parts, and the search proceeds through multiple levels of CAMs. This nested structure reduces the area of individual CAMs while collectively providing comprehensive address translation functionality
2Productivity
If multiple SMMUs are employed to increase translation speed, then processing throughput is improved, but chip area and resource utilization deteriorate
Solution Approach 1:
The patent merges multiple CAM searches into a unified hierarchical search structure. Instead of using separate SMMUs for different identifier segments, the invention combines them into a single coordinated search process across multiple CAM levels, reducing the need for multiple complete SMMU instances while maintaining parallel search capability
Solution Approach 2:
The patent transitions from a single-dimension search approach to a multi-dimensional hierarchical search. By organizing CAMs in a tree hierarchy with multiple levels, the system adds a dimensional aspect to the search process, allowing parallel searches to proceed through different paths in the hierarchy, thereby achieving high throughput without requiring multiple complete SMMU units
3Measurement precision
If the identifier is stored in full form in the CAM, then mapping accuracy is improved, but CAM area and search time deteriorate
Solution Approach 1:
The patent divides the full identifier into multiple segments and distributes them across different CAM locations. The high-order parts are stored in upper CAMs while low-order parts are stored in lower CAMs. This segmentation maintains complete identifier information for accurate mapping while reducing the area requirement of each individual CAM entry
Solution Approach 2:
The patent applies different storage strategies to different parts of the identifier based on their characteristics. High-order identifier parts that require broader matching are stored in upper CAMs with larger coverage, while low-order parts that require precise matching are stored in lower CAMs with more specific entries, optimizing both accuracy and area utilization
Data Source
AI summary
An embodiment of the present disclosure includes a method for compressing data for a translation look aside buffer (TLB). The method includes: receiving an identifier at a content addressable memory (CAM), the identifier having a first bit length; compressing the identifier based on a location within the CAM the identifier is stored, the compressed identifier having a second bit length, the second bit length being smaller than the first bit length; and mapping at least the compressed identifier to a physical address in a buffer.