Stream Open Implied Fence for DSP Cache Prefetch Stalls
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Solution Overview
Problem
Modern digital signal processors face challenges with increasing workloads, memory system latency, and scalability issues, particularly in streaming workloads, which are exacerbated by limited cache line retrieval and roundtrip latency, leading to performance bottlenecks and inefficiencies in memory systems.
Innovation Solution
The implementation of a streaming engine within the DSP that autonomously manages data streams, including address generation and data formatting, to improve processing efficiency and data scheduling, while utilizing a dual scalar/vector data path architecture with separate instruction and data caches to enhance bandwidth and reduce cache miss stalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the processor uses a traditional cache system to handle streaming workloads, then data storage capacity is improved, but memory system latency and cache miss stalls increase
Solution Approach 1:
The patent divides the cache system into separate instruction cache and data cache, and further segments the data cache into streaming data cache and non-streaming data cache. This segmentation allows streaming workloads to be handled by the dedicated streaming data cache with direct access paths, reducing cache miss stalls and memory latency while maintaining overall storage capacity.
2Productivity
If the processor increases bus bandwidth by widening the bus and increasing clock rate, then data transfer capability is improved, but wire routing complexity and latency increase
Solution Approach 1:
The patent introduces a new dimension to the data path architecture by creating separate streaming data paths that bypass the traditional hierarchical cache structure. Streaming data can be fetched directly from L2 cache to the streaming engine through dedicated paths, effectively adding a parallel dimension to data flow and achieving high bandwidth without increasing bus width or clock rate.
3Ease of operation
If the processor uses in-order execution to maintain simplicity, then ease of operation is improved, but ability to hide memory latency is worsened
Solution Approach 1:
The patent implements an autonomous streaming engine that independently manages streaming data fetches without requiring complex out-of-order execution logic in the main processor. The streaming engine self-manages its own data buffering, address generation, and prefetching operations, allowing the main processor to remain simple while latency is hidden through autonomous parallel operation.
Data Source
AI summary
Techniques related to executing a plurality of instructions by a processor comprising receiving a first instruction configured to cause the processor to output a first data value to a first address in a first data cache, outputting, by the processor, the first data value to a second address in a second data cache, receiving a second instruction configured to cause a streaming engine associated with the processor to prefetch data from the first data cache, determining that the first data value has not been outputted from the second data cache to the first data cache, stalling execution of the second instruction, receiving an indication, from the second data cache, that the first data value has been output from the second data cache to the first data cache, and resuming execution of the second instruction based on the received indication.