PCIe Endpoint Latency Management via Dynamic Power State Selection
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Solution Overview
Problem
The latency issue in PCIe links when transitioning from power-saving modes back to operational state causes delays, exceeding acceptable tolerances for some operating systems, leading to unexpected behavior and undesirable user experiences.
Innovation Solution
The endpoint informs the host of its operating system's latency tolerance and adjusts the PCIe link's power-saving mode accordingly, preventing entry into sub-states with excessive exit latency, ensuring the link remains in a state that meets the host's latency requirements, thereby managing power-saving modes to minimize latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the PCIe link enters a deeper power-saving mode to save more power, then power consumption is reduced, but the exit latency increases and may exceed acceptable tolerances
Solution Approach 1:
The endpoint dynamically adjusts the PCIe link power-saving state based on the host operating system's latency tolerance. The system transitions from static power management to dynamic state selection, where the endpoint monitors latency requirements and adjusts the power state accordingly, selecting between different L1 sub-states (L1.0, L1.1, L1.2) or remaining in L0 based on current latency constraints.
Solution Approach 2:
The endpoint changes the power state parameters of the PCIe link by informing the host of the operating system's latency tolerance and adjusting the power-saving mode accordingly. This involves modifying the link state selection based on latency tolerance parameters, preventing entry into sub-states with excessive exit latency while still utilizing appropriate power-saving states when acceptable.
2Use of energy by moving object
If the PCIe link remains in a power-saving mode to maintain low power consumption, then energy efficiency is improved, but system responsiveness deteriorates due to excessive latency
Solution Approach 1:
The system implements feedback by having the endpoint inform the host of the operating system's latency tolerance. This feedback mechanism allows the host to understand the latency constraints and adjust its communication patterns accordingly, while the endpoint can monitor and respond to latency requirements by adjusting power states, creating a closed-loop system that balances power consumption and responsiveness.
Solution Approach 2:
The system dynamically adjusts power states based on actual latency requirements rather than using a fixed power management policy. The endpoint can transition between different power states (L0, L1.0, L1.1, L1.2) dynamically based on the host's latency tolerance and current operational needs, optimizing both energy efficiency and system responsiveness in real-time.
3Loss of energy
If the PCIe link uses aggressive power-saving sub-states to maximize power savings, then power consumption is minimized, but the link may exceed allowable delay tolerances causing unexpected behavior
Solution Approach 1:
The endpoint changes the power state parameters by informing the host of the operating system's latency tolerance and adjusting the power-saving mode accordingly. This parameter adjustment prevents the system from entering power states that would cause unacceptable latency, thereby maintaining system reliability while still utilizing appropriate power-saving states.
Solution Approach 2:
The system takes preliminary action by having the endpoint inform the host of latency tolerance before the host initiates communication. This advance notification allows the host to plan communications appropriately and prevents the system from entering power states that would cause reliability issues, effectively preventing problems before they occur.
Data Source
AI summary
A method and system are described for reducing latency in a peripheral component interconnect express (PCIe) link between a host and an endpoint. In the described embodiments, an interrupt is issued from the endpoint to the host using the PCIe link. Then, while the interrupt is pending at the host, the PCIe link is prevented from entering a power-saving mode with an exit latency greater than a predetermined time period.