Granular CPU Power State Management via Timer Latency
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Solution Overview
Problem
Existing computing systems inefficiently manage CPU power consumption, leading to increased idle cycles and performance gaps between CPUs and I/O devices, as they rely on high-level assessments of idleness to transition into reduced power states, which can negatively impact system performance.
Innovation Solution
A method that transitions the CPU into a reduced power state based on a granular power reduction scheme, comparing latency with timer expiration times and aggregating signals to identify the most appropriate reduced power state for scheduled processing, allowing the CPU to enter a reduced power state during idle periods without impacting performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the CPU transitions into a reduced power state based on high-level idleness assessment, then power consumption is reduced, but system performance is negatively impacted due to excessive latency
Solution Approach 1:
The patent segments the idle time period into multiple intervals and divides reduced power states into different levels (first, second, third states with progressively greater power savings but also greater latency). The system selects the appropriate power state level based on the current interval and predicted idle continuation, preventing transitions to deep power states when recovery latency would exceed the remaining idle period.
Solution Approach 2:
The patent implements dynamic adjustment of power state transitions by continuously monitoring whether the CPU remains idle across multiple intervals. The system adapts the depth of power state transition based on real-time conditions, transitioning to deeper states only when idle periods are confirmed to be sufficiently long, and preventing transitions when latency would compromise performance.
2Productivity
If the CPU remains in a working state to avoid performance impact, then system performance is maintained, but power consumption increases during idle periods
Solution Approach 1:
The patent segments idle time into discrete intervals and uses this segmentation to make granular decisions about power state transitions. By evaluating idle conditions at each interval boundary and comparing against latency thresholds, the system achieves fine-grained control that prevents both excessive power consumption and performance degradation.
Solution Approach 2:
The patent changes the parameter of power state depth based on the duration of confirmed idle periods. The system monitors idle intervals and adjusts the power state transition depth dynamically, transitioning to deeper power states only when the idle period sufficiently exceeds the recovery latency threshold, thereby optimizing the balance between power savings and performance.
3Loss of energy
If deeper reduced power states are used to maximize power savings, then energy efficiency is improved, but recovery latency increases and impacts performance
Solution Approach 1:
The patent segments the power state reduction into multiple hierarchical levels (first reduced power state, second reduced power state, third reduced power state), where each level provides progressively greater power savings but also incurs progressively greater latency. The system selects the appropriate level based on the current idle interval duration, ensuring that the latency of the selected state does not exceed the remaining idle period.
Solution Approach 2:
The patent changes the power state depth parameter dynamically based on monitored idle conditions. By comparing the duration of confirmed idle intervals against the latency requirements of different power states, the system adjusts the power state transition depth to maximize savings while ensuring recovery can be completed before performance is needed.
Data Source
AI summary
Generally described, embodiments of the present invention are directed at reducing the power consumed by a CPU. In accordance with one embodiment, a method is provided that transitions the CPU into a reduced power state in response to a fetch operation being dispatched to an I/O device. More specifically, the method includes comparing the latency associated with recovering from a reduced power state with the time remaining before a timer expires. Then, a signal is generated that identifies a timer-specific reduced power state. The method aggregates signals received from different timers to identify a reduced power that is appropriate given all of the processing that is scheduled to be performed.