Shared Cache Accelerator Flag Data Transfer
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Solution Overview
Problem
Conventional solutions for offloading data from general purpose processing devices to hardware accelerators suffer from inefficiencies related to notifications, data exchange, and data sharing, including cache replacement policies that lead to data being marked as most-recently used even when it is not needed again.
Innovation Solution
Implementing a shared cache with LRU and accelerator flags to manage cache line reuse, and using monitors to efficiently exchange notifications between processors and accelerators, allowing for timely reuse of cache lines and preventing data from staying in the cache unnecessarily.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional cache replacement policies are used, then cache lines are managed automatically, but data is marked as most-recently used even when it will not be used further, reducing cache efficiency
Solution Approach 1:
An intermediary mechanism (the accelerator flag) is introduced between the cache replacement policy and the actual cache line management. This flag acts as a mediator that communicates the accelerator's intent regarding data usage, allowing the cache policy to make informed decisions about which lines to evict without being misled by premature LRU markings.
Solution Approach 2:
A feedback mechanism is implemented where the accelerator provides information back to the cache management system through the accelerator flag. This feedback loop allows the cache policy to adjust its behavior based on actual data usage patterns, preventing the marking of cache lines as LRU when the data is still needed by the accelerator.
2Speed
If data is kept in cache for accelerator processing, then data access is fast, but data remains in cache unnecessarily increasing energy consumption
Solution Approach 1:
The cache management system dynamically adjusts its behavior based on the state of the accelerator flag. When the flag indicates the accelerator needs data, the cache line is protected from eviction; when the flag is cleared, the cache line can be evicted. This dynamic adaptation allows the system to optimize between keeping data in cache for fast access and evicting data to save energy based on actual needs.
3Reliability
If notifications are exchanged between processor and accelerator, then data sharing coordination is improved, but communication overhead increases
Solution Approach 1:
The notification mechanism extracts only the essential information needed for coordination - the accelerator flag state - from complex inter-processor communication protocols. By taking out only the critical coordination signal rather than implementing full-blown notification exchanges, the system achieves reliable data sharing coordination with minimal communication overhead.
Data Source
AI summary
A processor writes input data to a cache line of a shared cache, wherein the input data is ready to be operated on by an accelerator. It then notifies an accelerator that the input data is ready to be processed. The processor then determines that output data of the accelerator is ready to be consumed, the output data being located at the cache line or an additional cache line of the shared cache, wherein the cache line or the additional cache line comprises a set first flag that indicates the cache line or the additional cache line was modified by the accelerator and that prevents the output data from being removed from the cache line or the additional cache line until the output data is read by the processor. The processor reads and processes the output data from the cache line or the additional cache.