Spinlock Wake-Up List Prevents Missed Interrupts
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Solution Overview
Problem
In multithreaded programming, the existing management techniques for accessing devices can result in missed wake up calls due to the critical period between a process determining a device is busy and its state being set to wait, leading to performance issues when interrupts are turned off in multiprocessing environments.
Innovation Solution
The use of a spinlock and lock structure to manage access to device drivers, where a process acquires a lock, sets its state to waiting if the device is not ready, and releases the lock upon access or waiting, preventing concurrent execution and missed wake up calls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interrupts are turned off before accessing a device driver to prevent missed wake up calls, then the reliability of process state management is improved, but the productivity of the system decreases due to decreased interrupt performance
Solution Approach 1:
The process state is changed to waiting and the wake-up list is updated before the actual device access operation. This preliminary action ensures that when the device becomes ready, the wake-up mechanism can reliably notify the correct process, eliminating missed wake-ups without needing to disable interrupts.
Solution Approach 2:
A wake-up list data structure is introduced as an intermediary mechanism between the device driver and the process state management system. This intermediary allows reliable communication of wake-up events without requiring interrupt disablement, resolving the contradiction between reliability and productivity.
2Reliability
If interrupts are turned off in a multiprocessing environment to prevent race conditions, then the reliability of process state management is improved, but the productivity of the system decreases due to unacceptable performance degradation
Solution Approach 1:
The process state is updated to waiting and the wake-up list is modified before the device access operation executes. This preliminary state change ensures race-condition-free process management in multiprocessing environments while maintaining full interrupt functionality and system performance.
Solution Approach 2:
The wake-up list serves as an intermediary structure that enables reliable process state management across multiple processors without requiring interrupt disablement. This intermediary mechanism eliminates race conditions while preserving system productivity in multiprocessing environments.
3Speed
If the process state is set to waiting immediately upon finding the device busy, then the responsiveness of process state management is improved, but the reliability decreases due to the critical period where wake up calls may be missed
Solution Approach 1:
The process state is changed to waiting and the wake-up list is updated as a preliminary action before the device access operation. This ensures that even if the device becomes ready during the critical period, the wake-up mechanism can reliably notify the process without missing the wake-up call.
Solution Approach 2:
The wake-up list acts as an intermediary that bridges the critical period between finding the device busy and actually accessing it. This intermediary structure ensures reliable wake-up notification without requiring the process to wait until the device access completes.
Data Source
AI summary
In a methods and systems of controlling a process's access to a device driver, a lock may be used to establish a process wait state or to wake up one or more processes. A spinlock may be used to acquire a lock associated with a device driver. The lock includes a lock value representing the availability of the lock. If the lock value is a first value, the process acquires the lock and sets the lock value to a second value. Otherwise, the process returns to the step of using the spinlock to acquire the lock associated with the device driver. If the lock is acquired, the process accesses the device driver. If the device is not ready, the process is set to wait for the lock. Waiting for the lock comprises setting a field of the process to a pointer to the lock and setting a state of the process to waiting. After the device has been successfully accessed or the process has been set to wait for the lock, the lock is released typically by setting the lock value to the first value.