Thread-Specific CAM Enable Logic for TLB Power Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern processors consume significant dynamic power during translation lookaside buffer (TLB) searches due to the need to compare each content addressable memory (CAM) entry with the requested virtual address, even though only a subset of entries are relevant to the executing thread.
Innovation Solution
The implementation of a TLB with enable logic that restricts CAM searches to only the entries associated with the executing thread, using mask vectors to enable only relevant CAM entries during a query, thereby reducing power consumption by limiting the number of entries searched.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all CAM entries are searched during every TLB query, then complete address translation coverage is ensured, but dynamic power consumption increases significantly
Solution Approach 1:
The patent segments the CAM into multiple sets, where each set is associated with a specific thread. The enable logic selectively activates only the CAM set corresponding to the querying thread, dividing the search space from a single large CAM into multiple smaller, thread-specific CAM sets. This segmentation reduces the number of entries searched while maintaining complete coverage for the active thread.
Solution Approach 2:
The patent applies partial action by searching only a subset of CAM entries rather than all entries. The enable logic determines which CAM entries are relevant to the current thread and activates only those entries for the search operation. This partial search approach maintains reliability for the active thread while reducing overall power consumption.
2Use of energy by moving object
If enable logic is added to selectively enable CAM entries, then power consumption is reduced, but device complexity increases
Solution Approach 1:
The patent introduces enable logic as an intermediary component between the TLB query mechanism and the CAM entries. This enable logic acts as a mediator that receives the thread identifier, determines which CAM set is relevant, and activates only the corresponding CAM entries. The intermediary approach manages the complexity by centralizing the selection logic rather than embedding complex control in each CAM entry or throughout the entire CAM structure.
3Use of energy by moving object
If CAM search is limited to thread-associated entries only, then power consumption decreases, but search time may increase due to multiple search phases
Solution Approach 1:
The patent applies preliminary action by pre-associating each CAM entry with a specific thread identifier during CAM entry creation or update. The enable logic uses these pre-established associations to quickly determine which CAM entries are relevant to the current thread before initiating the search. This preliminary organization eliminates the need for complex runtime analysis and enables rapid selection of the relevant CAM set, reducing search time despite the multi-phase nature of the operation.
Data Source
AI summary
An apparatus and method for saving power during TLB searches is disclosed. In one embodiment, a TLB includes a CAM having a plurality of entries each storing a virtual address, and enable logic coupled to the CAM. Responsive to initiation of a TLB query by a thread executing on a processor that includes the TLB, the enable logic is configured to enable only those CAM entries that are associated with the initiating thread. Entries in the CAM not associated with the thread are not enabled. Accordingly, an initial search of the TLB for responsive to the query is conducted only in the CAM entries that are associated with the thread. Those CAM entries that are not associated with the thread are not searched. As a result, dynamic power consumption during TLB searches may be reduced.