Walk Ahead Circuitry for Address Translation Latency Reduction
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Solution Overview
Problem
Modern data processing systems face significant latency issues due to the multiple stages of address translation required for memory access requests, which necessitate multiple accesses to the memory device, increasing latency and performance bottlenecks.
Innovation Solution
The introduction of walk ahead circuitry between the address translation circuitry and the memory device, which detects page table walk requests and generates prefetch memory requests to pre-fetch data or descriptors, thereby reducing latency by making necessary data available before it is explicitly requested.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If multiple levels of page tables are used for address translation, then the memory device size can be managed, but the latency increases due to multiple memory accesses
Solution Approach 1:
The patent implements a walk ahead circuit that performs preliminary actions by detecting page table walk requests and proactively initiating subsequent page table walks before the current walk completes. This allows the system to pre-fetch descriptor information from higher-level page tables while lower-level walks are still in progress, thereby reducing the overall address translation latency without changing the fundamental multi-level page table structure
2Measurement precision
If page table walk requests are processed sequentially, then the address translation is accurate, but the processing speed decreases
Solution Approach 1:
The patent introduces dynamic parallel processing capabilities through the walk ahead circuit, which can initiate multiple page table walk requests simultaneously based on detected patterns and requirements. The system dynamically adjusts the processing flow by overlapping sequential operations, maintaining accuracy through proper request ordering and validation while improving speed through concurrent execution of independent walk operations
3Loss of time
If prefetching mechanisms are implemented, then future access latency is reduced, but the complexity of the address translation circuitry increases
Solution Approach 1:
The walk ahead circuit operates autonomously by monitoring the address translation pipeline and automatically initiating prefetch operations when it detects page table walk requests. The circuit self-manages the timing and sequencing of prefetch operations without requiring external control signals or complex coordination logic, thereby reducing prefetching latency while minimizing the increase in circuitry complexity
Data Source
AI summary
A data processing apparatus and method are provided for performing address translation in response to a memory access request issued by processing circuitry of the data processing apparatus and specifying a virtual address for a data item. Address translation circuitry performs an address translation process with reference to at least one descriptor provided by at least one page table, in order to produce a modified memory access request specifying a physical address for the data item. The address translation circuitry includes page table walk circuitry configured to generate at least one page table walk request in order to retrieve the at least one descriptor required for the address translation process. In addition, walk ahead circuitry is located in a path between the address translation circuitry and a memory device containing the at least one page table. The walk ahead circuitry comprises detection circuitry used to detect a memory page table walk request generated by the page table walk circuitry of the address translation circuitry for a descriptor in a page table. In addition, the walk ahead circuitry has further request generation circuitry which is used to generate a prefetch memory request in order to prefetch data from the memory device at a physical address determined with reference to the descriptor requested by the detected memory page table walk request. This prefetched data may be another descriptor required as part of the address translation process, or may be the actual data item being requested by the processing circuitry. Such an approach can significantly reduce latency associated with the address translation process.