Cache-to-Register Prefetch Promotion for Lower Load-Use Latency
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Solution Overview
Problem
The delay in load-use latency, or the time between when a load micro-operation begins execution and when dependent micro-operations can proceed, is a significant concern in processors due to the need for data to be fetched from cache memories into processor registers, leading to inefficiencies in processor operation.
Innovation Solution
A processor implementation that includes a promotion logic functional block to speculatively promote prefetched data from a first-level data cache to physical registers, reducing the reliance on load micro-operations to provide data by monitoring cache blocks and promoting prefetched data to registers based on specific conditions, thereby making it available for dependent micro-operations without waiting for load completion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is loaded from cache memory to processor registers using load micro-operations, then data is made available for dependent micro-operations, but load-use latency increases due to the sequential dependency between load completion and dependent operation execution
Solution Approach 1:
The patent applies preliminary action by promoting prefetched data from the L1 data cache to physical registers before the data is actually needed by dependent micro-operations. The promotion logic monitors cache blocks and promotes prefetched data to registers in advance, so that when dependent operations are ready to execute, the data is already available in the register file rather than waiting for load micro-operations to complete.
Solution Approach 2:
The patent introduces promotion logic as an intermediary component between the L1 data cache and the register file. This promotion logic functional block monitors cache blocks, identifies prefetched data, and promotes it to physical registers, thereby mediating the data flow and eliminating the sequential dependency that causes load-use latency.
2Adaptability or versatility
If load micro-operations are used to fetch data from cache to registers, then data can be loaded on-demand, but processor execution is stalled during the load operation
Solution Approach 1:
The promotion logic performs preliminary action by promoting prefetched data to registers before it is needed by dependent operations. This allows the processor to maintain execution throughput because data is already prepared in registers when dependent operations are ready to execute, eliminating execution stalls that would occur with traditional on-demand loading.
Solution Approach 2:
The patent ensures continuity of useful action by having the promotion logic continuously monitor cache blocks and promote prefetched data to registers as soon as it becomes available. This continuous promotion process ensures that data is always ready in registers when needed, maintaining steady processor execution without interruptions or stalls.
3Productivity
If prefetched data is promoted to physical registers, then load-use latency is reduced and execution blocks remain busy, but additional monitoring and promotion logic is required
Solution Approach 1:
The promotion logic functional block performs multiple functions: it monitors cache blocks for prefetched data, identifies which data should be promoted, and actually promotes the data to physical registers. By combining these functions into a single multi-functional block, the patent reduces overall system complexity while achieving the benefits of reduced load-use latency and improved execution efficiency.
Data Source
AI summary
An electronic device includes a processor, the processor having a cache memory, a set of physical registers, and a promotion logic functional block. When one or more promotion conditions are met, the promotion logic functional block promotes prefetched data from a portion of a cache block in the cache memory to a physical register among the set of physical registers. For promoting the prefetched data, the promotion logic functional block acquires the prefetched data from the portion of the cache block and stores the prefetched data in the physical register.