Start/Stop Circuit for Performance Counter Event Timing
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Solution Overview
Problem
Current performance counters in computer systems are limited in their ability to collect data from multiple portions of the performance monitor bus simultaneously and cannot accurately measure the time between occurrences of events, which hinders advanced debugging and performance assessment.
Innovation Solution
A general-purpose performance counter circuit that allows multiple counters to access the same data on the performance monitor bus and includes edge detect, duration Min/Max, and start/stop circuit enhancements to track clock cycles and capture minimum or maximum durations between events, enabling simultaneous data access and event timing measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If each performance counter is assigned to a preselected portion of the PMB, then data collection is simplified and reliable, but multiple counters cannot simultaneously access the same data portion and event timing cannot be measured
Solution Approach 1:
The performance counter is enhanced with a start/stop circuit that enables it to perform multiple functions: traditional data counting from preselected PMB portions and new event timing measurement by stopping on subsequent events. This multi-functionality allows the same counter hardware to serve both purposes without requiring separate dedicated counters for each function.
Solution Approach 2:
The counter's operational mode is made dynamic through the start/stop circuit. The counter can transition between counting mode (incrementing on clock cycles) and timing mode (stopping on event occurrences). This dynamic behavior allows flexible adaptation to different measurement needs while using the same hardware resources.
2Measurement precision
If performance counters use traditional counting methodology, then implementation is straightforward, but they cannot accurately measure time between event occurrences
Solution Approach 1:
The start/stop circuit is configured to assert a stop signal upon detecting a specific event pattern. This preliminary action prepares the counter to automatically halt counting at the precise moment the target event occurs, enabling accurate timing measurement without requiring complex post-processing or external intervention.
Solution Approach 2:
The start/stop circuit acts as an intermediary between the performance monitor bus and the counter. It intercepts event signals from the PMB, processes them according to configured criteria, and controls the counter's operation accordingly. This intermediary layer adds measurement capability without requiring direct modification of the counter's core counting mechanism.
Data Source
AI summary
A circuit for tracking a number of clock cycles between occurrences of an event of interest. The circuit includes logic for asserting a run signal responsive to a first occurrence of the event of interest, logic for deasserting the run signal responsive to a second occurrence of the event of interest, and logic for incrementing a count value on each clock cycle while the run signal is asserted.