Atomic Page Table Entry Bit Updates for Fault-Free Address Translation
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Solution Overview
Problem
Existing processor systems face inefficiencies due to page faults caused by non-atomic updates of page table entry status bits, particularly in systems with multiple processes accessing shared memory, leading to performance degradation and increased latency.
Innovation Solution
Implement techniques for atomic updating of page table entry status bits by using a memory management unit (MMU) and load store unit (LSU) to perform read-modify-write operations atomically, ensuring that updates to status bits such as the accessed (A) bit and dirty (D) bit are synchronized across processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-atomic updates of page table entry status bits are used, then device complexity is reduced, but processor performance deteriorates due to page faults
Solution Approach 1:
The patent combines the read and write operations for page table entry status bits into a single atomic operation. The MMU performs both reading the current status bits and updating them simultaneously, eliminating the window for race conditions while maintaining straightforward hardware implementation through unified control logic in the MMU and LSU.
Solution Approach 2:
The patent introduces an intermediary validation mechanism where the LSU reads the page table entry status bits and compares them against expected values before allowing updates. This intermediary check prevents erroneous updates from causing page faults, acting as a mediator between the MMU's update requests and the actual page table modification.
2Reliability
If non-atomic updates are performed, then ease of operation is improved, but system reliability deteriorates due to memory coherency issues
Solution Approach 1:
The patent merges the read and write operations for page table entry status bits into a single atomic operation. The MMU performs both reading the current status bits and updating them simultaneously, eliminating the window for race conditions while maintaining straightforward hardware implementation through unified control logic in the MMU and LSU.
Solution Approach 2:
The patent introduces an intermediary validation mechanism where the LSU reads the page table entry status bits and compares them against expected values before allowing updates. This intermediary check prevents erroneous updates from causing page faults, acting as a mediator between the MMU's update requests and the actual page table modification.
3Productivity
If atomic updating operations are implemented, then productivity is improved by preventing page faults, but device complexity increases due to synchronization requirements
Solution Approach 1:
The patent combines the read and write operations for page table entry status bits into a single atomic operation. The MMU performs both reading the current status bits and updating them simultaneously, eliminating the window for race conditions while maintaining straightforward hardware implementation through unified control logic in the MMU and LSU.
Solution Approach 2:
The patent introduces an intermediary validation mechanism where the LSU reads the page table entry status bits and compares them against expected values before allowing updates. This intermediary check prevents erroneous updates from causing page faults, acting as a mediator between the MMU's update requests and the actual page table modification.
4Reliability
If atomic operations are used for PTE updates, then reliability is improved, but loss of time increases due to additional read-modify-write cycles
Solution Approach 1:
The patent combines the read and write operations for page table entry status bits into a single atomic operation. The MMU performs both reading the current status bits and updating them simultaneously, eliminating the window for race conditions while maintaining straightforward hardware implementation through unified control logic in the MMU and LSU.
Solution Approach 2:
The patent introduces an intermediary validation mechanism where the LSU reads the page table entry status bits and compares them against expected values before allowing updates. This intermediary check prevents erroneous updates from causing page faults, acting as a mediator between the MMU's update requests and the actual page table modification.
Data Source
AI summary
A processor core is accessed. The processor core supports virtual memory addressing. The processor core includes a memory management unit (MMU) and a load store unit (LSU). A page table walk is performed by the MMU. The page table walk is responsive to a memory operation. The page table walk identifies a page table entry (PTE) for a virtual to physical address translation. The PTE is read. The reading obtains a first value from the PTE and includes determining, by the MMU, to update one or more status bits within the PTE. The PTE is re-read. The re-reading obtains a second value from the PTE. The PTE is updated to include the one or more status bits, based on a match between the first and second value. The updated PTE is stored in a page table. The re-reading, the updating, and the storing are performed atomically.