Coherence Trap Unit for Memory Value Detection
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Solution Overview
Problem
Existing shared memory multiprocessing systems face challenges in ensuring coherence, with hardware mechanisms being complex and costly to implement, while software approaches offer flexibility but lower performance.
Innovation Solution
A processor with a coherence trap unit and trap logic detects designated values to initiate coherence traps, ensuring cache coherence by signaling a processor to trap to software routines, and a cache system with a control unit detects cache tags indicating coherence traps to maintain data consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hardware coherence mechanisms are implemented, then coherence reliability is improved, but device complexity and implementation cost increase
Solution Approach 1:
The patent introduces a software coherence manager as an intermediary layer between hardware and software components. This manager handles coherence protocols through software routines, reducing the need for complex hardware coherence mechanisms while maintaining reliability through a dedicated software component that mediates between processors and memory systems
Solution Approach 2:
The system changes the state of cache lines to a designated value (e.g., invalidated or special marker state) to indicate coherence traps. This parameter change allows the system to signal coherence issues without requiring complex hardware detection mechanisms, as the software can detect and respond to these designated values in cache tags
2Adaptability or versatility
If purely software coherence mechanisms are used, then flexibility and ease of repair are improved, but performance decreases
Solution Approach 1:
The patent segments the coherence management function into two parts: hardware components (coherence trap unit, cache tags with designated value detection) that provide fast detection and signaling, and software components (coherence manager, software routines) that handle the actual coherence protocols. This segmentation allows performance-critical detection to occur in hardware while flexible protocol implementation occurs in software
Solution Approach 2:
The coherence trap unit acts as a hardware intermediary that detects designated values and triggers traps to software routines. This intermediary provides fast hardware-based detection and signaling while delegating the complex coherence management logic to software, combining the speed of hardware with the flexibility of software
3Reliability
If hardware coherence mechanisms are implemented, then coherence enforcement is improved, but design time and repair cost increase
Solution Approach 1:
The patent uses simple, easily implementable hardware structures such as cache tags with designated value detection and coherence trap units that can be quickly designed and modified. These hardware components are kept simple and focused on detection and signaling, while the complex coherence logic is implemented in software that can be easily updated without hardware changes
Solution Approach 2:
The software coherence manager serves as a mediator that handles complex coherence logic in software, allowing hardware to remain simple and focused on fast detection. This separation makes the system easier to manufacture and repair, as software can be updated to fix coherence issues without requiring complex hardware modifications
Data Source
AI summary
In one embodiment, a processor comprises a coherence trap unit and a trap logic coupled to the coherence trap unit. The coherence trap unit is also coupled to receive data accessed in response to the processor executing a memory operation. The coherence trap unit is configured to detect that the data matches a designated value indicating that a coherence trap is to be initiated to coherently perform the memory operation. The trap logic is configured to trap to a designated software routine responsive to the coherence trap unit detecting the designated value. In some embodiments, a cache tag in a cache may track whether or not the corresponding cache line has the designated value, and the cache tag may be used to trigger a trap in response to an access to the corresponding cache line.