Cache Coherence Validation Using Delayed L2 Request Fulfillment
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Solution Overview
Problem
In multithread and multicore processors, maintaining cache coherence across multiple processing elements is challenging due to the complexity of ensuring accurate read and write operations in shared memory devices, and existing software-based solutions are costly and require frequent redesigns to accommodate changing computer architectures.
Innovation Solution
A method and system that includes a processing element with a load store unit capable of detecting load instructions and applying a delay to data transfers from a global memory location to a local memory location, allowing for the validation of cache coherence by creating out-of-order hazards and re-executing younger load instructions to ensure sequential consistency, utilizing hardware components that can be selectively activated for validation purposes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If software-based solutions are used to maintain cache coherence, then cache coherence can be validated, but development costs increase and frequent redesigns are required
Solution Approach 1:
The patent replaces software-based cache coherence validation with a hardware-based solution. Specifically, it introduces a validation unit with delay logic that operates in hardware to detect and validate cache coherence violations, eliminating the need for costly software-based validation approaches and their associated frequent redesigns
Solution Approach 2:
The patent introduces a validation unit as an intermediary component between processing elements and shared memory devices. This validation unit includes delay logic that mediates the validation process by introducing controlled delays to detect out-of-order completions, providing a dedicated hardware mechanism for cache coherence validation without requiring software intervention
2Reliability
If hardware validation components are added, then cache coherence validation capability is improved, but device complexity increases
Solution Approach 1:
The patent segments the validation function into a separate validation unit that is selectively activatable. The validation unit is divided into distinct components including delay logic, detection logic, and control signals, allowing the system to add validation capability without permanently increasing the complexity of the entire processor structure
Solution Approach 2:
The patent uses parameter changes by introducing variable delay periods that can be adjusted based on validation needs. The validation unit can modify timing parameters dynamically, allowing flexible validation without requiring fixed complex hardware structures for all possible validation scenarios
3Reliability
If delay is applied to data transfer, then out-of-order hazards are created for validation, but data transfer time increases
Solution Approach 1:
The patent implements periodic validation delays rather than continuous delays. The delay logic introduces delays only during validation periods when validation signals are active, allowing normal fast data transfer during non-validation periods. This periodic approach creates out-of-order hazards for validation while maintaining overall data transfer efficiency
Solution Approach 2:
The patent applies preliminary delays to specific data transfers before validation occurs. By introducing delays in advance to selected transfers, the system creates controlled out-of-order scenarios that enable validation of coherence logic without delaying all data transfers, thus maintaining overall system performance
Data Source
AI summary
Methods and systems for validating cache coherence in a data processing system are described. A processing element may detect a load instruction requesting the processing element to transfer data from a global memory location to a local memory location. The processing element may apply, in response to detecting the load instruction requesting the processing element to transfer data from the global memory location to the local memory location, a delay to the transfer of the data from the global memory location to the local memory location. The processing element may execute the load instruction and transferring the data from the global memory location to the local memory location with the applied delay. The processing element may validate, in response to executing the load instruction and transferring the data with the applied delay, a cache coherence of the data processing system.