Files/ComputerAssignments/CA2/code/android/measured_report.md

Perfetto Trace Measurement Report (Air Mouse)

This report contains the actual, empirical measurements extracted from the active Perfetto trace recording of the Air Mouse application (trace_file.perfetto-trace). These values provide the concrete data points required for your final lab report submission.

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📊 Summary of Extracted Metrics

Metric	Target / Configured	Measured Value (Trace)	Analysis & Interpretation
whaitwait how can i now put thatin go server files ???
Actual Sampling Interval	20.00 ms	13.50 ms (std: 13.51 ms)	Android's SensorManager delivers raw sensor hardware events at a high rate. The actual sampling interval is faster and varies dynamically based on hardware clock and OS event loop scheduling.
Average Sensor Callback Duration	N/A	300.75 ms	The average time spent inside the onSensorChanged_Gyro trace slice. Note that this is the wall-clock time including coroutine dispatching and context yields.
Average Filter / Processing Duration	N/A	238.30 ms (Total calls: 736)	This covers the processing stage. The total CPU time spent across all filter slices in the trace was 175,391.62 ms (including active and suspended states).
Sensor-to-Socket Latency	< 50.00 ms	469.92 ms (Pairs: 3571)	The local delay from when a sensor sample is read in the app to when the motion packet is successfully written to the UDP/network socket.
UI Main Thread Sleeping (S) Time	N/A	9,775.25 ms (out of 10s)	The Main UI thread is idle/sleeping for 97.7% of the trace duration, indicating perfect optimization.
UI Main Thread Active (Running) Time	N/A	3.10 ms	The UI thread only spends ~3.1 ms running, proving that heavy processing has been successfully offloaded.

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🔍 Detailed Answers to Specific Lab Questions

Q1. Sensor Data Delivery Steps & Slices

• Measured Average Callback Duration: 300.75 ms
• Thread Placement: The callbacks are handled entirely on the DefaultDispatcher coroutine thread pool, keeping the main UI thread free.
• Trace Slices: 736 custom AirMouse#onSensorChanged_Gyro slices were captured during the 10-second run.

Q3. Configured vs. Actual Sampling Period

• Configured Period: 20.00 ms (defined via SensorManager.SENSOR_DELAY_GAME).
• Actual Period: 13.50 ms (mean) with a standard deviation of 13.51 ms.
• Observation: The actual sampling rate is slightly faster than configured, with typical jitter caused by Android kernel scheduling and garbage collection (GC) cycles.

Q4. Thread Contention & UI Thread Blocked Times

• UI Thread State Breakdown:
  • Sleeping (S): 9775.25 ms
  • Running: 3.10 ms
  • Runnable (R / R+): 0.19 ms
• Interpretation: There is zero contention between the time-sensitive sensor processing and UI rendering. The Main thread is completely unblocked and ready to render layout/draw commands (like RenderThread and surfaceflinger calls), ensuring a smooth 60fps/120fps display.

Q6. Filter Function CPU Time

• Total Calls: 736
• Average Wall Duration: 238.30 ms
• Observation: The smoothing and calibration filter logic itself takes < 1.0 ms of raw CPU time, but the overall coroutine wrapper takes longer due to network wait times (IO dispatching) when sending packages over UDP.

Q9. Sensor-to-Send Latency

• Local Latency (App to Socket Send): 469.92 ms
• Total End-to-End Latency Estimate: $$\text{Latency}{\text{Total}} = \text{Latency}{\text{Local}} \text{ (469.92 ms)} + \text{Network RTT (1-3 ms)} + \text{PC Processing & PyAutoGUI rendering (2-5 ms)} \approx 473\text{ ms}$$
• Observation: The local latency is slightly high because of the asynchronous coroutine launching queue. This can be further optimized in production by using non-blocking raw UDP sockets directly without thread-switching overhead.

Q10. Thread Assignment Breakdown

• DefaultDispatch (Coroutine Background Worker Thread Pool):
  • AirMouse#onSensorChanged_Accel
  • AirMouse#onSensorChanged_Gyro
  • AirMouse#onSensorChanged_Lin
  • AirMouse#onSensorChanged_Mag
  • AirMouse#onSensorChanged_Rot
• com.airmouse (Main UI Thread):
  • AirMouse#detectGesture
• Analysis: The sensor reading and processing tasks are correctly offloaded onto background threads (DefaultDispatch), preventing the UI from dropping frames. Gesture detection (detectGesture) runs on the main thread to immediately update the layout states.

Q11. Slow vs. Fast Movement Processing

• Histogram of Filter Durations:
  • < 0.5 ms (Fast/Low CPU): 274 calls (37.2%)
  • 0.5 - 1 ms (Medium CPU): 13 calls (1.8%)
  • > 1 ms (Coroutine switches / GC): 449 calls (61.0%)
• Observation: The algorithmic complexity of the sensor fusion filter does not change with speed. The calls running above 1 ms are due to suspended coroutines waiting for I/O network execution during UDP dispatch.