TLB Lease Mechanism for Multi-Core Latency Reduction
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Solution Overview
Problem
The latency associated with TLB shootdowns in computing devices is high, particularly in systems with multiple processors, leading to delays and inefficiencies in memory operations.
Innovation Solution
Implementing a separate translation lookaside buffer (TLB) in each processor core with lease values and latest lease values to avoid unnecessary TLB shootdowns by determining the validity of cached entries, allowing for dynamic lease length determination and extension counters to manage lease expiration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TLB shootdown is performed to modify page table entries in multi-processor systems, then consistency between processors is maintained, but latency increases significantly
Solution Approach 1:
The patent applies preliminary action by setting a lease value when caching page table entry information in the TLB before any modification occurs. This lease value establishes a predetermined time window during which the cached information remains valid. When the lease expires, the system knows in advance that invalidation may be needed, allowing the initiating processor to proactively check lease status and invalidate entries before inconsistencies arise, rather than reacting to consistency problems after they occur.
Solution Approach 2:
The patent implements dynamics by making the TLB entry validity dynamic through time-based lease values instead of static invalidation. The lease value creates a dynamic validity period that automatically transitions entries from valid to invalid state over time. This dynamic approach allows the system to adapt to changing conditions without requiring continuous active management or immediate shootdown operations, reducing latency while maintaining consistency.
2Measurement precision
If TLB shootdown is performed frequently to maintain consistency, then data accuracy is improved, but processing speed decreases
Solution Approach 1:
The patent applies periodic action by using time-based lease values that automatically expire after predetermined intervals. Instead of continuously checking or frequently invalidating TLB entries, the system establishes periodic validity windows through lease values. This periodic approach ensures data accuracy by systematically refreshing or invalidating entries at regular intervals while minimizing the frequency of shootdown operations, thereby maintaining processing speed.
Solution Approach 2:
The patent implements self-service by making TLB entries self-validating through their lease values. Each cached entry carries its own expiration timestamp, allowing the system to automatically determine validity without continuous external intervention. The lease mechanism enables entries to effectively manage their own validity state, reducing the need for frequent processor-initiated shootdowns and improving overall processing efficiency while maintaining data accuracy.
Data Source
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AI summary
The described embodiments include a computing device with two or more translation lookaside buffers (TLB). During operation, the computing device updates an entry in the TLB based on a virtual address to physical address translation and metadata from a page table entry that were acquired during a page table walk. The computing device then computes, based on a lease length expression, a lease length for the entry in the TLB. Next, the computing device sets, for the entry in the TLB, a lease value to the lease length, wherein the lease value represents a time until a lease for the entry in the TLB expires, wherein the entry in the TLB is invalid when the associated lease has expired. The computing device then uses the lease value to control operations that are allowed to be performed using information from the entry in the TLB.