Processor Power Management Unit Idle State Transition
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Solution Overview
Problem
Modern processors face challenges in managing power consumption and latencies when entering and exiting idle power states, as deeper idle power states often require higher power during entry and exit phases, which can be impractical due to timing constraints and increased latency, limiting their usage.
Innovation Solution
Incorporating a power management unit that selects appropriate performance states based on the requested idle power state to reduce power consumption and latency, allowing processors to transition into and out of idle states more efficiently by operating at higher or lower frequencies as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the processor enters deeper idle power states to reduce power consumption, then power consumption is reduced, but entry and exit latencies increase and require higher power during transition phases
Solution Approach 1:
The processor transitions to a preliminary performance state (e.g., P3) before entering the idle power state. This preliminary action prepares the processor by operating at a lower frequency that is more suitable for the transition, thereby reducing the entry latency and power consumption spike associated with deeper idle states.
Solution Approach 2:
The system dynamically adjusts the performance state based on the target idle power state. When transitioning to deeper idle states (e.g., C6), the processor dynamically selects an appropriate preliminary performance state (P3) rather than using a fixed performance state, allowing flexible optimization of both latency and power consumption based on the specific idle state being entered.
2Use of energy by moving object
If the processor enters deeper idle power states to reduce power consumption, then power consumption is reduced, but power consumption during entry and exit phases increases
Solution Approach 1:
The processor performs a preliminary transition to a performance state optimized for the upcoming idle state entry. By transitioning to P3 before entering C6, the processor avoids the high power spike that would occur if directly entering from an active state, thereby reducing the total energy loss during the transition phase.
Solution Approach 2:
The system changes the performance state parameters (frequency, voltage) based on the target idle state. When entering deeper idle states, the processor changes to a lower frequency performance state (P3) that matches the power requirements of the idle state, thereby reducing the power consumption during the transition and eliminating unnecessary power spikes.
3Loss of time
If the processor uses higher performance states to reduce entry and exit latency, then latency is reduced, but power consumption increases
Solution Approach 1:
The system dynamically selects the appropriate performance state based on the target idle power state rather than always using the highest performance state. For deeper idle states, it dynamically chooses a lower performance state (P3) that reduces power consumption while still providing acceptable latency, thereby optimizing the trade-off between latency and power consumption.
Solution Approach 2:
The processor changes its operating parameters (performance state) based on the specific idle state being entered. Instead of using a fixed high-performance state for all transitions, the system adjusts the performance state parameters to match the requirements of the target idle state, reducing unnecessary power consumption while maintaining acceptable latency performance.
Data Source
AI summary
Techniques are disclosed relating to managing power consumption and latencies for entry and exit of idle power states. In one embodiment, a processor includes a processing core configured to operate in a plurality of power states (e.g., C-states) that includes an operating power state and at least one idle power state. The processing core is also configured to operate in a plurality of performance states. The processor further includes a power management unit configured to receive a request from the processing core to enter the at least one idle power state. The power management unit is configured to select a first of the plurality of performance states (e.g., P-states) based on the requested idle power state. In one embodiment, the power management unit is further configured to cause the processing core to transition into the selected first performance state prior to entering the requested idle power state.