Tree-Based Trylock for RCU Memory Contention
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Solution Overview
Problem
In large systems with many processors, existing read-copy update (RCU) implementations face extreme memory contention due to high rates of attempts to acquire the global quiescent state forcing lock, leading to reduced throughput and sub-optimal energy efficiency.
Innovation Solution
A tree-based trylock operation is implemented to reduce contention on the root trylock by distributing trylocks among nodes of a tree-based node structure, allowing processors to be assigned to leaf nodes in a balanced manner, and attempting to acquire trylocks along a traversal path from leaf to root, with all non-root trylocks released if the acquisition fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global quiescent state forcing lock is used in RCU implementations, then data consistency is maintained, but memory contention increases and throughput decreases in large systems with many processors
Solution Approach 1:
The patent divides the single global quiescent state forcing lock into multiple hierarchical trylocks distributed across a tree structure. Each processor is assigned to a leaf node and acquires trylocks along the path to the root, segmenting the centralized locking mechanism into distributed hierarchical locks that reduce contention while maintaining data consistency.
2Reliability
If a global quiescent state forcing lock is used in RCU implementations, then data consistency is maintained, but energy efficiency deteriorates due to redundant acquisition attempts
Solution Approach 1:
The patent segments the global locking operation into hierarchical trylocks distributed across the tree structure. This segmentation eliminates redundant acquisition attempts by allowing processors to acquire locks in a structured manner along their traversal paths, reducing wasted energy while preserving data consistency through the hierarchical locking mechanism.
3Productivity
If trylocks are distributed among tree nodes with processors assigned to leaf nodes, then memory contention is reduced, but device complexity increases
Solution Approach 1:
The patent implements a nested hierarchical structure where trylocks are organized in a tree with processors at leaf nodes and root trylock at the top. This nesting allows the system to manage complexity through hierarchical organization, where each level of the tree encapsulates a subset of the locking logic, reducing memory contention while keeping the overall structure manageable.
Solution Approach 2:
The patent transitions from a single-dimension global lock to a multi-dimensional hierarchical tree structure. By organizing trylocks across multiple levels and dimensions of the tree, the system reduces contention through spatial distribution while managing complexity through the structured hierarchical arrangement.
Data Source
AI summary
A tree-based trylock technique for reducing contention on a root trylock includes attempting to acquire a trylock at each node of a tree-based hierarchical node structure while following a traversal path that begins at a leaf node, passes through one or more of internal nodes, and ends at a root node having the root trylock. The trylock acquisition operation succeeds if each trylock on the traversal path is acquired, and fails if any trylock on the traversal path cannot be acquired. A trylock housekeeping operation releases all non-root trylocks visited by the trylock acquisition operation, such that if the trylock acquisition operation succeeds, only the root trylock will be remain acquired at the end of the operation, and if the trylock acquisition operation fails, none of the trylocks will be remain acquired at the end of the operation.