TLB Invalidation Latency Optimization via Range-Based Entry Traversal
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Solution Overview
Problem
Current computing systems face inefficiencies in cache maintenance due to high latency when invalidating multiple entries in a translation lookaside buffer (TLB), leading to delays in processing instructions and potential denial-of-service situations.
Innovation Solution
Implementing a method called 'long invalidation' where the cache controller determines if the first latency to invalidate all entries is greater than the second latency to invalidate each entry individually, allowing for reduced processing time by searching only the relevant TLB entries instead of traversing all addresses, and 'short invalidation' for cases where the first latency is less, optimizing the approach based on latency comparison.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cache controller traverses all addresses in the range to invalidate TLB entries, then all relevant entries are guaranteed to be invalidated, but the processing latency increases significantly
Solution Approach 1:
The patent segments the address range into multiple pages, and further segments the TLB entries into groups that can be invalidated together. By organizing TLB entries by their page number fields and using bit masks to identify groups of entries that share common page number bits, the system processes invalidation in manageable segments rather than traversing every individual address sequentially.
Solution Approach 2:
The patent performs preliminary actions by pre-calculating bit masks that identify groups of TLB entries sharing common page number characteristics. Before actual invalidation, the system determines which entry groups fall within the invalidation range using these pre-computed masks, allowing for efficient batch invalidation without逐一 checking each address.
2Loss of time
If the cache controller processes maintenance requests with high priority to reduce latency, then instruction processing delay is minimized, but the local instruction stream is blocked during maintenance request servicing
Solution Approach 1:
The patent implements dynamic behavior by allowing the cache controller to switch between different invalidation strategies based on the characteristics of the maintenance request. When a range-based invalidation request is received, the system dynamically determines whether to use traditional address-by-address traversal or the optimized page-based group invalidation method, adapting its processing approach to minimize both latency and instruction stream blocking.
3Measurement precision
If the TLB is searched multiple times to determine which entries to invalidate, then accurate identification of invalidation candidates is achieved, but the receiving processor cannot achieve forward progress on the local instruction stream
Solution Approach 1:
The patent merges multiple TLB entry validation operations into a single efficient process. By combining the page number comparison with group-based entry identification using bit masks, the system identifies all invalidation candidates in one pass through the TLB entries rather than performing separate searches for each address in the range, thereby maintaining accuracy while enabling instruction stream progress.
Data Source
AI summary
A system and method for efficiently performing maintenance on a cache. In various embodiments, control logic in a cache controller or elsewhere receives an indication for invalidating a range of virtual-to-physical mappings in a given translation lookaside buffer (TLB). The logic determines a first latency to invalidate entries of the TLB based on a number of addresses in the range and a number of supported page sizes simultaneously stored in the TLB. The logic determines a second latency based on a number of entries in the TLB. If the first latency is greater, then the logic traverses through each TLB entry and invalidates TLB entries storing a virtual address within the range. If the first latency is smaller, then the logic traverses through each address in the range and invalidates TLB entries storing a virtual address within the range.