Memory Module Context Switching via Link Prefetch
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Solution Overview
Problem
In existing context switching techniques, it is difficult to predict the next task during interrupt processing, leading to delays in context information recovery due to the inability to hold context information in register banks for tasks unrelated to the current one.
Innovation Solution
A memory module with an access control circuit that writes context information and link context numbers to storage units during interrupts, allowing for efficient restoration of context information by identifying and prefetching the correct context data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If context information is stored in register banks for fast access, then context switching speed is improved, but context information for interrupt-related tasks cannot be held when the next task is unpredictable
Solution Approach 1:
The patent applies preliminary action by prefetching context information into the buffer group before it is actually needed. When an interrupt occurs, the access control circuit identifies the link context number and prefetches the corresponding context information into the buffer group in advance, so that when the task needs to resume, the context is already available for rapid restoration without waiting for external memory access.
2Loss of time
If context information is prefetched into buffer group, then context restoration time is reduced, but memory module complexity increases
Solution Approach 1:
The patent applies the nested doll principle by creating a hierarchical memory structure where the buffer group (faster, smaller) is nested within the external memory system (slower, larger). The buffer group acts as an intermediate layer that holds frequently accessed context information, while the external memory retains the complete context database. This nested architecture enables fast context restoration for interrupt-related tasks while maintaining the comprehensive storage capacity of the external memory system.
3Measurement precision
If link context number is stored and used for prefetching, then context identification accuracy is improved, but data storage requirements increase
Solution Approach 1:
The patent applies the taking out principle by extracting only the essential link context number from the complete context information and storing it separately in the buffer group. Instead of prefetching entire context structures, the system stores compact context identifiers (link context numbers) that serve as keys to retrieve the actual context information from external memory when needed. This extraction approach maintains high context identification accuracy while minimizing the storage space required in the buffer group.
Data Source
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AI summary
The access control circuit writes to the first storage unit a context information transmitted in one cycle from the CPU through the first bus, a context number identifying the context information, and a link context number identifying the context information transmitted from the CPU prior to the interrupt when the request for evacuating the task context information is received by the interrupt. After writing to the first storage unit, the access control circuit transfers the data including the context information and the link context number stored in the first storage unit to the second storage unit in a plurality of cycles through the internal bus (second bus) in association with the context number stored in the first storage unit.