TLB Tag Mapping via Hashed Identifier Segmentation
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Solution Overview
Problem
The increasing number of address bits in virtual address spaces and tag spaces leads to increased latency in translation lookaside buffers (TLBs) due to wider comparisons, which affects processor performance.
Innovation Solution
A system comprising registers and a control unit that maps changed tags to identifiers with fewer bits, reducing the number of bits compared in TLB lookups, thereby improving TLB performance by supporting multiple virtual address spaces without the slower comparisons of larger tags.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of address bits in virtual address space increases, then the capability to support larger memory spaces is improved, but the TLB comparison width increases causing higher latency
Solution Approach 1:
The patent segments the tag comparison function into two parts: a hashed identifier comparison (smaller, faster) and a full tag comparison (larger, more accurate). The TLB is divided into entries that store both a hashed identifier and the full tag, allowing a two-stage lookup process that reduces the critical path delay while maintaining full address space support
Solution Approach 2:
The patent introduces a hashed identifier as an intermediary element between the full virtual address and the TLB entry. This intermediary serves as a quick-filter key that narrows down the search space before performing the complete tag comparison, effectively mediating between the need for fast lookup and the need to handle large address spaces
2Adaptability or versatility
If the tag width increases to support more virtual address spaces, then the number of supported address spaces increases, but the comparison time increases
Solution Approach 1:
The patent changes the parameter used for initial comparison from the full tag width to a hashed identifier width. By transforming the tag through a hashing function to produce a smaller identifier, the system can perform faster comparisons while still maintaining the ability to distinguish between multiple virtual address spaces through the combination of hashed identifier and full tag verification
Data Source
AI summary
In one embodiment, a system comprises one or more registers configured to store a plurality of values that identify a virtual address space (collectively a tag), a translation lookaside buffer (TLB), and a control unit coupled to the TLB and the one or more registers. The control unit is configured to detect whether or not the tag has changed and in response to a change in the tag, map the changed tag to an identifier having fewer bits than the total number of bits in the tag, and provide the current identifier to the TLB. The TLB is configured to detect a hit/miss in response to the identifier. A similar method is also contemplated.