Interrupt Steering and Idle State Demotion for CPU Latency
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Solution Overview
Problem
Existing computing systems statically assign processor units to handle interrupts, leading to performance degradation, increased latency, and power consumption due to inefficient idle state transitions, particularly affecting high-performance cores handling interrupts.
Innovation Solution
Dynamic interrupt steering and idle state demotion techniques that dynamically reassign interrupts to high-efficiency processor units and avoid deep idle states, reducing preemption of critical processes and minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a processor unit is designated to handle interrupt types and placed in deep idle state for power savings, then power consumption is reduced, but latency and power idle state exit costs increase when transitioning to active state
Solution Approach 1:
The patent implements dynamic interrupt steering that adapts processor unit assignments based on real-time workload characteristics and processor state. The system dynamically selects between static affinity-based routing and dynamic remapping based on interrupt characteristics, workload type, and processor utilization, allowing the system to optimize between power savings and latency response on-demand
Solution Approach 2:
The system changes the operational parameters of processor units by monitoring workload utilization rates and adjusting interrupt remapping decisions accordingly. When processors are underutilized, the system allows deeper idle states for power savings; when utilization increases or latency-sensitive workloads are detected, the system remaps interrupts to active processors, dynamically adjusting system behavior based on parameter thresholds
2Reliability
If high-performance processor units are designated to handle interrupts, then interrupt handling capability is improved, but system performance and user experience degrade due to preemption of critical threads
Solution Approach 1:
The patent applies different interrupt handling strategies to different processor units based on their current workload characteristics. Instead of uniformly assigning all interrupts to high-performance cores, the system evaluates each processor's current state and workload type, directing interrupts to processors with appropriate capabilities for that specific interrupt type, thereby preserving high-performance core capacity for critical threads while maintaining reliable interrupt handling
Solution Approach 2:
The system dynamically adjusts interrupt remapping decisions based on real-time monitoring of processor utilization rates and workload characteristics. The interrupt handling capability is adapted on-demand rather than being statically assigned, allowing the system to maintain reliability by routing interrupts to suitable processors while preventing preemption of critical threads on high-performance units when they are engaged in important workloads
3Device complexity
If static interrupt steering approaches are used, then system simplicity is maintained, but adaptability to processor capabilities and real-time characteristics is lost
Solution Approach 1:
The patent implements a hybrid approach that maintains static affinity-based interrupt routing as the default simple mechanism while introducing dynamic remapping capabilities that activate based on monitored conditions. The system transitions between static and dynamic modes depending on workload characteristics and processor state, preserving simplicity when possible while enabling adaptability when needed
Solution Approach 2:
The system incorporates feedback mechanisms that monitor processor utilization rates, workload characteristics, and interrupt handling performance. This feedback informs dynamic remapping decisions, allowing the system to adapt to processor capabilities and real-time characteristics while maintaining a relatively simple base architecture that only becomes complex when adaptation is required
Data Source
AI summary
Dynamic interrupt steering remaps the handling of interrupts away from processor units executing important workloads. During the operation of a computing system, important workload utilization rates for processor units handling interrupts are determined and those processor units with utilization rates about a threshold value are made unavailable for handling interrupts. Interrupts are dynamically remapped to processor units available for interrupt handling based on processor unit idle state and, in the case of heterogeneous computing systems, processor unit type. Processor units are capable of idle state demotion by, in response to receiving a request to enter into a deep idle state, determining if its interrupt handling rate is greater than a threshold value, and if so, placing itself into a shallower idle state than requested. This avoids the computing system from incurring the expensive idle state exit latency and power costs associated with exiting from a deep idle state.