Speculative Address Translation in Processors to Reduce DMA Page Faults
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Solution Overview
Problem
Peripheral devices encounter page faults due to physical memory pages being paged out during Direct Memory Access (DMA) operations, leading to increased latency and reduced throughput, which conventional methods like pinning or pre-touching are inefficient or inconsistent with programming models.
Innovation Solution
Implementing speculative address translation in processor-based devices through a memory-pointer-referencing (MPR) instruction that performs speculative translation of virtual memory addresses, raising exceptions if errors occur, allowing for asynchronous or synchronous error handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional address translation is used during DMA operations, then memory access can be performed, but page faults occur when physical memory pages are paged out, increasing latency and reducing throughput
Solution Approach 1:
The system performs speculative address translation before the actual DMA operation occurs. When an MPR instruction is executed, the processor initiates address translation in advance and determines whether the target memory page is resident. This preliminary action allows the system to prepare for potential page faults before they impact DMA throughput, resolving the contradiction by proactively handling address translation issues.
2Reliability
If memory pages are pinned to ensure residency, then page faults are reduced, but this approach increases device complexity and goes against efficient work offloading goals
Solution Approach 1:
The processor automatically performs speculative address translation and determines page residency status without requiring external intervention or complex memory management mechanisms. This self-service approach resolves the contradiction by providing reliable page residency detection through automated processor actions rather than complex system-wide pinning mechanisms.
3Reliability
If pre-touching memory pages is performed to ensure residency, then page faults may be reduced, but this requires additional processor work and may pollute caches
Solution Approach 1:
The system merges the address translation operation with the MPR instruction execution flow. Instead of performing separate pre-touching operations that add extra processor work and cache pollution, the address translation is combined into the normal instruction execution path. This resolves the contradiction by achieving page residency verification without additional standalone operations.
4Loss of time
If speculative address translation is performed through MPR instruction, then page fault occurrence is reduced and latency is minimized, but exception handling mechanisms are required
Solution Approach 1:
The system uses an intermediary exception handling mechanism that captures address translation results and communicates them to the appropriate software layer. This intermediary approach resolves the contradiction by providing a structured way to handle translation outcomes without requiring complex error handling logic throughout the entire system.
Data Source
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AI summary
Performing speculative address translation in processor-based devices is disclosed herein. In one exemplary embodiment, a processor-based device provides a processing element (PE) that defines a speculative translation instruction such as an enqueue instruction for offloading operations to a peripheral device. The speculative translation instruction references a plurality of bytes including one or more virtual memory addresses. After receiving the speculative translation instruction, an instruction decode stage of an execution pipeline circuit of the PE transmits a request for address translation of the virtual memory address to a memory management unit (MMU) of the PE. The MMU then performs speculative address translation of the virtual memory address into a corresponding translated memory address. In some embodiments, any address translation errors encountered are raised to an appropriate exception level, and may be raised synchronously or asynchronously with respect to an operation performed when the speculative translation instruction is executed.