Collaborative Page Fault Handling via Intermediate Buffer
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Solution Overview
Problem
In cloud service environments, page faults occur due to the race condition between CPU and device page fault handling threads, leading to incorrect data retrieval from intermediate buffers, as the CPU retrieves page content before the page fault is resolved, causing data inconsistency and inefficiency in address translation.
Innovation Solution
A collaborative page fault handling framework is introduced, where an intermediate overflow buffer manages page faults for Virtual Functions, allowing multiple sources to coordinate and handle page faults once, using an API for callback registration in kernel space to synchronize CPU and device drivers, and employing a page fault table to manage translations and resolve faults efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If CPU and device page fault handling threads operate independently, then each can handle page faults autonomously, but race conditions occur leading to incorrect data retrieval and data inconsistency
Solution Approach 1:
The patent introduces an intermediate buffer as a mediator between the CPU and device memory spaces. When a page fault occurs, data is first stored in this intermediate buffer, which then coordinates the data transfer to the final destination. This intermediary mechanism prevents race conditions by providing a controlled handoff point, ensuring that data is only retrieved after the page fault is fully resolved and the intermediate buffer is properly populated.
2Speed
If CPU retrieves page content before page fault is resolved, then data access speed is improved, but incorrect data is retrieved from intermediate buffers causing data inconsistency
Solution Approach 1:
The patent implements preliminary action by pre-populating the intermediate buffer with the required page content before the CPU retrieves the data. The system anticipates the data transfer need and prepares the intermediate buffer in advance, ensuring that when the CPU needs the data, it is already available in the correct location. This eliminates the race condition where the CPU might retrieve incorrect or incomplete data.
3Adaptability or versatility
If multiple sources handle page faults independently, then page fault handling flexibility is improved, but race conditions between CPU and device handlers cause inefficiency and data inconsistency
Solution Approach 1:
The patent merges the page fault handling operations of multiple sources (CPU and device) into a coordinated process centered around the intermediate buffer. Instead of allowing independent handling that leads to conflicts, the system combines their efforts by having both the CPU and device interact with the shared intermediate buffer under controlled conditions. This unified approach maintains the flexibility of multiple handlers while eliminating race conditions through synchronized access.
Data Source
AI summary
As described herein, for a selected process identifier and virtual address, a page fault arising from multiple sources can be solved by a one-time operation. The selected process identifier can include a virtual function (VF) identifier or process address space identifier (PASID). In some examples, solving a page fault arising from multiple sources by a one-time operation comprises invoking a page fault handler to determine an address translation.