Timer Rate Limiting via Coalescing Windows for Power Reduction
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Solution Overview
Problem
Modern computing devices face increased power consumption and reduced opportunities for low power modes due to frequent interrupts from multiple timers, which necessitate techniques to maintain low power states while still providing timer functionality.
Innovation Solution
The method involves coalescing timer execution by scheduling timers within scheduling windows and opportunistically executing timers based on trigger events, as well as rate-limiting lower priority timers to reduce the frequency of interrupts, thereby minimizing power consumption and maintaining low power modes for longer periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple timers are executed individually at their scheduled times, then each timer is executed timely and accurately, but the number of interrupts increases and power consumption increases
Solution Approach 1:
The patent merges multiple individual timer executions into a single coalesced timer execution. When multiple timers are scheduled to execute within a coalescing window, they are combined into one interrupt that executes all coalesced timers simultaneously. This reduces the total number of interrupts and allows the device to remain in low power mode longer, directly addressing the contradiction between timely timer execution and power consumption.
2Use of energy by moving object
If timers are coalesced and rate-limited to reduce interrupts, then power consumption is reduced and low power modes are extended, but timer execution timing may be delayed
Solution Approach 1:
The patent implements dynamic timer coalescing where timers are grouped into coalescing windows based on their execution timing and priority. The system dynamically adjusts which timers are coalesced together and when they execute, rather than using fixed scheduling. This dynamic approach allows the system to optimize for power savings while ensuring that high-priority timers are executed with minimal delay and low-priority timers can be safely delayed for power savings.
Solution Approach 2:
The patent applies different coalescing and rate-limiting strategies to timers based on their priority levels. High-priority timers are given preferential treatment with smaller coalescing windows and less aggressive rate-limiting, ensuring timely execution. Low-priority timers accept larger coalescing windows and more aggressive rate-limiting to maximize power savings. This localized quality approach resolves the contradiction by treating different timers differently based on their importance.
3Use of energy by stationary object
If the device enters low power mode frequently, then power consumption is reduced, but timer interrupts cause frequent wake-ups and reduce low power mode duration
Solution Approach 1:
The patent uses preliminary action by establishing coalescing windows before timers are executed. Multiple timers are pre-grouped into coalescing windows based on their scheduled execution times and priorities. This preliminary grouping allows the system to predict when multiple timers will need to execute and prepare coalesced execution slots in advance. As a result, the device can enter low power mode knowing that multiple timer executions will be handled efficiently in coalesced groups, extending the low power mode duration while ensuring all timers are executed.
Data Source
AI summary
A method and apparatus of a device that rate-limits the execution of a timer is described. The device receives a timer that includes an initial execution timer and a timer priority. If the timer priority is low, the device rate-limits the execution of the timer based on a suppression period associated with the timer priority. In order to rate-limit the execution of the timer, the device determines the suppression period based on the timer priority and schedules the timer to execute at the end of the suppression period. The device further schedules the timer to execute at the initial exertion time when the timer priority is high.