Indirect Memory Fetch Unit for Sparse Operand Access
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Solution Overview
Problem
Existing processor architectures are inefficient in handling indirect memory accesses due to irregular and sparse access patterns, leading to wasted cache capacity and memory bandwidth, and increased latency, which hinders performance in big data analysis and other applications.
Innovation Solution
An indirect memory fetch unit is introduced to offload indirect memory accesses from the processing engine, autonomously fetching data from memory and storing it in a FIFO queue, allowing the processor to perform other tasks while waiting for data, thus improving cache and memory bandwidth usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional caching systems are used for indirect memory accesses, then cache capacity is utilized, but cache efficiency deteriorates due to irregular access patterns and data eviction before reuse
Solution Approach 1:
The patent extracts the indirect memory access function from the conventional caching system by introducing a dedicated indirect memory fetch unit. This specialized unit handles irregular access patterns separately, allowing the main cache to focus on regular access patterns where it is effective, thereby resolving the contradiction between cache capacity utilization and cache efficiency.
Solution Approach 2:
The memory access system is segmented into two paths: conventional caching for regular access patterns and a dedicated indirect memory fetch unit for irregular patterns. This segmentation allows each component to optimize for its specific workload, improving overall system efficiency while maintaining cache capacity utilization.
2Reliability
If threads wait for data from main memory, then data accuracy is ensured, but processing speed deteriorates due to halted threads
Solution Approach 1:
The indirect memory fetch unit performs preliminary actions by autonomously fetching data from main memory in advance and storing it in a FIFO queue. This allows processing threads to continue execution without waiting for memory data, as the fetch unit proactively prepares data beforehand, thus maintaining data accuracy while improving processing speed.
Solution Approach 2:
A FIFO queue is introduced as an intermediary buffer between main memory and processing threads. The indirect memory fetch unit populates this queue autonomously, allowing threads to consume data at their own pace without blocking on memory access, thereby decoupling data accuracy requirements from processing speed constraints.
3Loss of time
If dedicated prefetching hardware is added, then memory latency is hidden, but device complexity increases
Solution Approach 1:
The indirect memory fetch unit operates autonomously without requiring complex control logic from the main processor. It self-manages fetching data from main memory, storing indices, calculating addresses, and populating the FIFO queue, thereby hiding memory latency while adding minimal complexity to the overall system architecture.
Data Source
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AI summary
Disclosed embodiments relate to an indirect memory fetch (IMF) unit. In one example, an apparatus includes circuitry to fetch and decode an instruction specifying a sparse operand array including N operands, and an index array including N contiguously-addressed indices. The apparatus further includes a processing engine associated with an IMF unit to respond to the decoded instruction by initializing the IMF unit to fetch the N operands in order, probing the IMF unit to determine that a fetched operand is ready to retrieve, retrieving the fetched operand from the IMF unit, and repeating the probing and retrieving until all N operands have been retrieved. The IMF unit, independent of the processing engine, is to fetch the N contiguously-addressed indices from the index array, use the N fetched indices to calculate memory addresses for the N operands, and issue a plurality of read requests to fetch the N operands in order.