System Management Interrupt Telemetry for Latency Debugging
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Solution Overview
Problem
Existing information handling systems lack effective methods for collecting system management interrupt (SMI) telemetry, making it difficult to identify and debug SMI-related issues that can cause performance glitches such as audio or video playback interruptions, especially during lengthy SMI tasks.
Innovation Solution
Implementing a system management interrupt telemetry mechanism that includes an SMI handler to log timestamps at entry and exit points of SMIs, calculate latency, and store data in a buffer or CPLD register, enabling collection of SMI count, duration, and latency for analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SMI telemetry collection is implemented, then troubleshooting capability for SMI-related issues is improved, but system complexity increases due to additional logging and measurement mechanisms
Solution Approach 1:
The patent introduces an SMI handler as an intermediary component that sits between the SMI execution path and the telemetry collection mechanism. This handler automatically logs entry/exit timestamps and calculates latency without requiring changes to the core SMI handling logic or application code, thus improving troubleshooting capability while minimizing system complexity
Solution Approach 2:
The telemetry collection system is designed to be self-configuring and self-managing. The SMI handler automatically enables telemetry collection, manages its own buffer allocation, and performs self-diagnosis by comparing timestamps. This eliminates the need for external configuration or manual intervention, offsetting the added complexity through automation
2Loss of information
If detailed SMI telemetry data is collected and stored, then diagnostic information quality is improved, but memory usage increases due to buffer and register storage requirements
Solution Approach 1:
The patent segments the telemetry data storage into two distinct parts: a buffer for storing detailed SMI event information and a CPLD register for storing critical latency metrics. This segmentation allows the system to collect comprehensive diagnostic information while managing memory usage by storing only essential data in the hardware register and detailed data in the software buffer
Solution Approach 2:
The system implements partial telemetry collection by selectively logging only the most critical SMI parameters (entry timestamp, exit timestamp, and calculated latency) rather than capturing every possible SMI detail. This partial action approach provides sufficient diagnostic information while minimizing memory consumption
3Measurement precision
If SMI latency calculation is performed for every SMI event, then measurement precision is improved, but processing overhead increases during SMI handling
Solution Approach 1:
The patent implements preliminary action by pre-allocating buffer space and pre-configuring the SMI handler to automatically capture timestamps at entry and exit points. This preparation eliminates the need for runtime memory allocation or complex measurement logic during SMI handling, maintaining measurement precision while minimizing processing overhead
Solution Approach 2:
The patent replaces complex software-based latency measurement mechanisms with a simpler timestamp-difference calculation approach. By using hardware-supported timestamp counters and performing simple subtraction to calculate latency, the system achieves precise measurements without the overhead of more sophisticated timing mechanisms
Data Source
AI summary
An information handling system receives a system management interrupt (SMI), and if an SMI telemetry is enabled, then the system reads a first timestamp at an entry point of the SMI. Subsequent to handling the SMI, the system reads a second timestamp at an exit point of the SMI, and calculates a system management mode latency based on a difference between the second timestamp at the exit point and the first timestamp at the entry point.