Processor Idle State Correction Using Residency Timer Transitions

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Solution Overview

Problem

Modern processors with multiple cores face idle state misprediction due to the dynamic nature of future sleep duration predictions, leading to inefficiencies in power management and increased overhead in kernel low power management selection.

Innovation Solution

A system and method that automatically transitions hardware entities from a selected idle state to a deeper idle state when a hysteresis timer associated with the deeper state expires, eliminating the need for reevaluation and reducing overhead.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If dynamic idle hints are used to select desired idle states based on predicted sleep duration, then power management efficiency is improved, but idle state misprediction occurs leading to increased overhead

Engineering Contradiction:

Improvepower management efficiencyVSAvoidoverhead in kernel low power management selection

Core Design Contradiction:

Use of energy by moving objectVSLoss of time

Solution Approach 1:

The system performs preliminary action by issuing a WFI instruction to trigger entry into the selected idle state before the actual wake-up event occurs. The residency timer is configured in advance to automatically transition to a deeper idle state if the predicted sleep duration is exceeded, eliminating the need for runtime reevaluation and reducing overhead.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements self-service through automatic correction mechanisms. When idle state misprediction is detected (when the predicted sleep duration is exceeded), the system automatically transitions to the appropriate deeper idle state without requiring kernel intervention or reevaluation, thereby reducing overhead while maintaining power management efficiency.

Inventive Principle:

Principle #25Self-service

2Loss of energy

If deeper idle states are selected to maximize power savings, then energy consumption is reduced, but the risk of misprediction increases requiring reevaluation overhead

Engineering Contradiction:

Improvepower savingsVSAvoidreevaluation overhead

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The system performs preliminary action by pre-configuring the residency timer before entering the idle state. The timer is set to automatically trigger a transition to a deeper idle state if the predicted sleep duration is exceeded, eliminating the need for runtime reevaluation and reducing overhead while maintaining the ability to maximize power savings.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements feedback through the residency timer mechanism that monitors the actual sleep duration against the predicted duration. When the timer expires (indicating misprediction), the system automatically provides corrective action by transitioning to the appropriate deeper idle state, thereby maintaining power savings without requiring complex reevaluation procedures.

Inventive Principle:

Principle #23Feedback

3Loss of energy

If automatic transition to deeper idle state is implemented when residency timer expires, then power savings are improved, but the system complexity increases

Engineering Contradiction:

Improvepower savingsVSAvoidsystem complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The system implements self-service through the automatic correction mechanism. When the residency timer expires (indicating idle state misprediction), the system automatically transitions to the appropriate deeper idle state without requiring external intervention or complex control logic, thereby improving power savings while minimizing the increase in system complexity.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The system applies parameter changes by dynamically adjusting the idle state based on the residency timer expiration. When the timer expires, the system changes the idle state parameter from the currently selected state to a deeper idle state, providing an simple yet effective mechanism to improve power savings without significantly increasing system complexity.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20260064182A1System and method for correction of hardware entity idle state misprediction

Publication Date: 2026.03.05 QUALCOMM INC

AI summary

A method for correction of idle state misprediction is described. The method includes receiving an indication of a selected idle state based on a predicted sleep duration of a hardware entity. The method also includes issuing a wait for interrupt (WFI) instruction to the hardware entity to trigger entry into the selected idle state. The method further includes transitioning the hardware entity to a deeper idle state if a residency timer associated with the deeper idle state is expired prior to a wake-up of the hardware entity from the selected idle state.