Asymmetric SMP Signal Merging Tree for Cache Coherence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current symmetric multiprocessing (SMP) systems face scalability limitations due to intrinsic and explicit scalability limitations, primarily caused by data dependencies, thread coordination overhead, and cache coherence maintenance, which restrict the potential speedup and efficiency of parallel processing.
Innovation Solution
The implementation of an asynchronous SMP architecture using a signal merging tree structure and a traversal mechanism for serializing concurrent requests, along with a broadcast-free, latency-hiding coherence protocol that employs push and pull instructions and unaccepted invalidation bits to manage cache lines, allowing for incoherent views of the address space and reducing the need for synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional SMP cache coherence protocols are used to maintain consistent views of shared memory across processors, then data consistency is ensured, but coordination overhead and cache coherence traffic increase significantly, limiting scalability
Solution Approach 1:
The patent segments the monolithic cache coherence protocol into fine-grained, localized coherence operations. Instead of maintaining global consistency across all processors, coherence is maintained locally within processor groups or for specific memory regions, reducing the overhead of coordination while ensuring data consistency where required by the program semantics.
Solution Approach 2:
The patent inverts the traditional approach by allowing processors to have incoherent views of shared memory by default, and only establishing coherence when explicitly required by synchronization operations or memory semantics. This reverses the conventional model where coherence is maintained continuously and proactively, transforming it into a reactive, demand-driven mechanism that reduces unnecessary coordination overhead.
2Reliability
If synchronous synchronization mechanisms are used to coordinate access to shared memory, then data consistency is maintained, but latency increases and processor utilization decreases
Solution Approach 1:
The patent employs preliminary actions by pre-establishing coherence protocols for frequently accessed memory regions or by pre-synchronizing data before it becomes critical. This allows processors to access shared memory with minimal latency while maintaining consistency, as the coordination overhead has already been performed in advance rather than at the moment of access.
Solution Approach 2:
The patent implements periodic synchronization mechanisms where coherence is maintained at specific intervals or triggered by specific events rather than continuously. This periodic approach reduces the average synchronization latency by allowing processors to operate independently between synchronization points, while still ensuring data consistency when needed.
3Reliability
If broadcast-based coherence protocols are used to invalidate cache lines across all processors, then cache coherence is maintained, but network traffic and processing overhead increase
Solution Approach 1:
The patent applies local quality by making cache coherence invalidation targeted and localized rather than universal. When a cache line is invalidated, the protocol identifies and notifies only the specific processors that have cached copies of that line, rather than broadcasting to all processors in the system. This reduces coherence traffic and energy consumption while maintaining coherence for the affected memory regions.
Solution Approach 2:
The patent introduces intermediary structures such as directory-based coherence mechanisms or cache coherence agents that mediate between processors and manage invalidation traffic. These intermediaries track which processors have cached copies of memory lines and route invalidation messages only to the relevant processors, reducing overall network traffic and processing overhead compared to universal broadcasting.
4Productivity
If the number of processors in an SMP system is increased to improve parallel processing capability, then computational power increases, but scalability is limited by coordination overhead and coherence maintenance
Solution Approach 1:
The patent addresses scalability by organizing processors into hierarchical groups or clusters, adding a dimensional structure to the processor architecture. This hierarchical organization allows coherence and synchronization operations to be performed locally within groups before propagating to higher levels, reducing the complexity growth that would otherwise occur with linear increases in processor count and enabling better scalability.
Data Source
AI summary
An apparatus for serializing concurrent requests to multiple processors includes a signal merging tree structure and a traversal mechanism. The tree structure has a root node and leaf nodes for connecting a data consumer to the root. The tree structure serializes concurrent requests in the presence of race conditions, and connects each request producer from among the processors to a respective leaf node. The mechanism enables a producer to transmit a signal from a corresponding leaf node to the consumer at the root node by setting all nodes on a path from the leaf node to the root node to a Boolean true. The mechanism enables the consumer to trace signal submissions of the producers such that submission traversals by the producers and trace traversals by the consumer can be concurrently performed to allow data races between signal submissions by producers and between signal submissions by producers and the consumer.