Early Wake Scheme for Processing Element Power State Transition
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Solution Overview
Problem
Current processing elements face increased overhead and reduced power savings due to deep sleep states, as deeper sleep states lead to longer wake-up times, resulting in a tradeoff between power savings and performance.
Innovation Solution
Implementing an early wake scheme that allows processing elements to transition to a lower power state before a new thread is spawned, reducing wake latency by providing an early wake indication, which can be software-generated or hardware-predicted, to minimize the time required to reach an active state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If processing elements are placed in deeper sleep states to save power, then power savings are increased, but wake-up time increases
Solution Approach 1:
The system performs preliminary actions by transitioning the processing element to an intermediate power state before the actual wake-up event. The early wake indication triggers a preliminary transition from the deep sleep state to a lighter sleep state or toward active state, so that when the actual wake-up occurs, the processing element is already partially prepared, reducing the total wake-up time while maintaining the power savings of the deep sleep state.
2Loss of energy
If processing elements are placed in deeper sleep states, then power savings are increased, but thread spawn overhead increases
Solution Approach 1:
The system uses early wake indications to perform preliminary transitions to lighter power states before thread spawn events. This allows the processing element to be partially ready when a thread needs to be spawned, reducing the overhead associated with waking from deep sleep states while maintaining the power efficiency benefits.
Solution Approach 2:
The system implements feedback mechanisms where the power management unit monitors wake-up conditions and adjusts power state transitions accordingly. When an early wake indication is detected, the system feedbacks by initiating a preliminary transition to an appropriate power state, ensuring optimal balance between power savings and thread spawn performance.
3Loss of time
If processing elements transition quickly from deep sleep states, then wake time is reduced, but power consumption during transition increases
Solution Approach 1:
The system segments the wake-up process into multiple stages by introducing intermediate power states. Instead of transitioning directly from deep sleep to full active state (which would consume high power during the transition), the system segments the transition through lighter sleep states or intermediate states, reducing the power consumption burden during each transition phase while still achieving quick wake-up.
Solution Approach 2:
The preliminary transition to intermediate power states performs part of the wake-up preparation in advance, allowing the processing element to reach a partially active state before the full wake-up event. This distributes the power consumption over time rather than concentrating it in a single high-power transition, reducing peak power consumption during wake-up.
Data Source
AI summary
An apparatus and method is described herein for providing an early wake scheme before spawning a new thread. An early wake indication may be provided an amount of time, which may include an amount of time to perform a demotion from a current power state to a lower power state that is closer to an active power state, before a new thread is to be spawned and executed on a processing element (e.g., core or thread). Upon encountering the spawn of the new thread, such as a helper thread, the processing element may further transition from the lower power state to an active power state. The new thread may be executed on the processing element without incurring the latency associated with execution of the new thread waiting for the demotion from the current power state to an active power state after the spawn of the new thread.