Performance Analyzer

Performance Analyzer

Monitor and optimize VoiceLite performance against strict targets.

When This Skill Activates

• Keywords: "slow", "memory leak", "high CPU", "performance", "optimization"
• Metrics mentioned: RAM, CPU, latency, FPS, responsiveness
• Violations: ">100MB idle", ">300MB active", ">5% CPU idle", "slow transcription"
• After changes to: AudioRecorder, PersistentWhisperService, MainWindow
• User reports: "App is slow", "High memory usage", "Laggy UI"

VoiceLite Performance Targets

From CLAUDE.md - these are STRICT requirements:

All targets are non-negotiable - VoiceLite must be lightweight and responsive.

Quick Performance Check

Manual Task Manager Method

# 1. Launch VoiceLite.exe

# 2. Wait 30 seconds (reach idle state)

# 3. Open Task Manager (Ctrl+Shift+Esc)
#    - Details tab → Find VoiceLite.exe
#    - Check "Memory (Private Working Set)"
#      ✓ Should be <100MB
#      ✗ If >150MB → Memory leak investigation needed

# 4. Check CPU usage over 30 seconds
#    ✓ Should average <5%
#    ✗ If >10% → CPU profiling needed

# 5. Test transcription
#    - Record 5 seconds of audio
#    - Check memory spike
#      ✓ Should stay <300MB
#      ✗ If >400MB → Audio buffer leak

# 6. Check whisper process
#    - After recording, check whisper.exe appears briefly
#    - Should disappear after <2s for tiny model
#    ✗ If lingers → Zombie process (disposal issue)

Automated Performance Tests

// VoiceLite.Tests/Performance/PerformanceTests.cs

[Fact]
public async Task TranscriptionLatency_ShouldBeLessThan200ms()
{
    // Arrange
    var recorder = new AudioRecorder();
    var whisper = new PersistentWhisperService();

    // Act
    var stopwatch = Stopwatch.StartNew();
    var audio = await recorder.Record5Seconds();
    var text = await whisper.TranscribeAsync(audio);
    stopwatch.Stop();

    // Assert
    stopwatch.ElapsedMilliseconds.Should().BeLessThan(200);
}

[Fact]
public void IdleMemory_ShouldBeLessThan100MB()
{
    // Arrange
    GC.Collect();
    GC.WaitForPendingFinalizers();
    GC.Collect();

    // Act
    var memoryMB = GC.GetTotalMemory(false) / 1024 / 1024;

    // Assert
    memoryMB.Should().BeLessThan(100);
}

[Fact]
public async Task WhisperProcessing_TinyModel_ShouldBeLessThan800ms()
{
    // Arrange
    var service = new PersistentWhisperService("ggml-tiny.bin");
    var test5sAudio = "test_audio_5s.wav";

    // Act
    var stopwatch = Stopwatch.StartNew();
    await service.TranscribeAsync(test5sAudio);
    stopwatch.Stop();

    // Assert
    stopwatch.ElapsedMilliseconds.Should().BeLessThan(800);
}

Memory Profiling with dotMemory

Installation

# Download JetBrains dotMemory (free 30-day trial)
# Or use dotMemory CLI for CI/CD

Profiling Workflow

# 1. Attach to running VoiceLite process
# Tools → Attach to Process → Select VoiceLite.exe

# 2. Take baseline snapshot (idle state)
# Wait 30s, click "Get Snapshot"

# 3. Perform 10 transcriptions

# 4. Take second snapshot

# 5. Compare snapshots
# Look for growing:
# - byte[] arrays (audio buffers not disposed)
# - Process objects (whisper zombies)
# - Event handlers (subscription leaks)

Red Flags in dotMemory

Growing byte[] arrays:

Snapshot 1: 1.5 MB byte[]
Snapshot 2: 15.2 MB byte[]

→ Audio buffers not being released
→ Check AudioRecorder.Dispose() called
→ Verify _audioBuffer cleared after use

Growing Process objects:

Snapshot 1: 0 Process instances
Snapshot 2: 10 Process instances

→ Whisper.exe processes not disposed
→ Check PersistentWhisperService.TranscribeAsync finally block
→ Ensure process?.Dispose() called

Growing event subscriptions:

Snapshot 1: 5 event handlers
Snapshot 2: 50 event handlers

→ Events subscribed but never unsubscribed
→ Check -= in Dispose methods
→ Example: _audioRecorder.AudioFileReady -= OnAudioFileReady

CPU Profiling with PerfView

Collect CPU Trace

# 1. Download PerfView.exe (free, Microsoft)
# https://github.com/microsoft/perfview/releases

# 2. Run as Administrator

# 3. Collect → Collect
# or command line:
PerfView.exe collect -ThreadTime

# 4. Perform actions in VoiceLite (transcriptions)

# 5. Stop collection

# 6. Analyze → CPU Stacks

Analyzing CPU Hotspots

Look for:

• High % in specific method → Optimization target
• Tight loops → Potential infinite loop or inefficiency
• Excessive GC → Too many allocations
• Blocking I/O on UI thread → Move to background

Example findings:

Method: AudioRecorder.ProcessBuffer - 45% CPU
→ Buffer processing inefficient
→ Optimization: Use Span<byte> instead of byte[]

Method: GC.Collect - 15% CPU
→ Too many allocations
→ Optimization: Reuse buffers, reduce new object creation

Common Performance Issues

Issue 1: Memory Leak in AudioRecorder

Symptom: RAM grows from 50MB → 200MB+ after 20 recordings

Diagnosis:

// Check if Dispose is called
public class AudioRecorder : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("AudioRecorder.Dispose called"); // Add logging
        _waveIn?.Dispose();
        _waveIn = null;
    }
}

// Check if actually disposed after use
using (var recorder = new AudioRecorder())
{
    await recorder.RecordAsync();
} // Should call Dispose here

Fix: Ensure using statement or explicit Dispose() call

Issue 2: Whisper Zombie Processes

Symptom: Multiple whisper.exe processes remain after transcription

Diagnosis:

# Check running whisper processes
tasklist | findstr whisper.exe

# Should be 0 when idle
# If >0 → Disposal issue

Fix:

// PersistentWhisperService.cs
public async Task<string> TranscribeAsync(string path)
{
    Process? process = null;
    try
    {
        process = new Process { /* ... */ };
        process.Start();
        // ...
    }
    finally
    {
        // CRITICAL: Always dispose
        process?.Kill(); // If still running
        process?.Dispose();
    }
}

Issue 3: UI Thread Blocking

Symptom: UI freezes during transcription

Diagnosis:

// Check if long-running work on UI thread
private void OnRecordButtonClick(object sender, RoutedEventArgs e)
{
    // ❌ BAD: Blocks UI thread
    var result = _whisperService.TranscribeAsync(audio).Result;

    // ✅ GOOD: Async/await keeps UI responsive
    var result = await _whisperService.TranscribeAsync(audio);
}

Fix: Use async/await throughout, never .Result or .Wait()

Issue 4: Large Audio Buffer Allocations

Symptom: Memory spikes during recording

Optimization:

// Before: New allocation every buffer
private void OnDataAvailable(object sender, WaveInEventArgs e)
{
    var buffer = new byte[e.BytesRecorded]; // Allocation!
    Buffer.BlockCopy(e.Buffer, 0, buffer, 0, e.BytesRecorded);
}

// After: Reuse buffer
private readonly byte[] _reusableBuffer = new byte[8192];
private void OnDataAvailable(object sender, WaveInEventArgs e)
{
    Buffer.BlockCopy(e.Buffer, 0, _reusableBuffer, 0, e.BytesRecorded);
}

Whisper Performance Optimization

Command-Line Flags (v1.0.85-88 Optimizations)

# Current optimized command (67-73% faster)
whisper.exe \
  -m ggml-tiny.bin \
  -f audio.wav \
  --no-timestamps \
  --language en \
  --beam-size 1 \        # Greedy decoding (fastest)
  --best-of 1 \          # Single pass
  --entropy-thold 3.0 \  # Early stopping
  --no-fallback \        # No secondary attempts
  --max-context 64 \     # Smaller context window
  --flash-attn           # Flash attention (12% faster)

# v1.0.84 command (baseline)
whisper.exe -m ggml-tiny.bin -f audio.wav --no-timestamps --language en
# ~2.5s for 5s audio

# v1.0.88 command (current)
# ~0.7s for 5s audio (67% faster!)

Model Performance Comparison

Performance Regression Testing

CI/CD Performance Tests

# Run performance tests in CI
dotnet test --filter "Category=Performance"

# Set environment variable for thresholds
PERFORMANCE_STRICT=true dotnet test

# Fail build if performance regresses

Benchmarking Script

# benchmark.ps1
$iterations = 10
$results = @()

for ($i = 0; $i -lt $iterations; $i++) {
    $sw = [Diagnostics.Stopwatch]::StartNew()

    # Test transcription
    ./VoiceLite/bin/Release/VoiceLite.exe --test-transcribe test_5s.wav

    $sw.Stop()
    $results += $sw.ElapsedMilliseconds
}

$avg = ($results | Measure-Object -Average).Average
Write-Host "Average transcription time: $avg ms"

if ($avg -gt 800) {
    Write-Error "Performance regression! Target: <800ms, Actual: $avg ms"
    exit 1
}

Optimization Checklist

Before releasing new version:

• Run performance tests: dotnet test --filter Performance
• Check idle RAM: Task Manager <100MB
• Check active RAM: Peak <300MB during transcription
• Profile with dotMemory: No growing byte[] or Process objects
• Check whisper zombies: tasklist | findstr whisper = 0 when idle
• Test transcription latency: <800ms for tiny model
• Verify CPU usage: <5% idle, <30% during transcription
• No UI blocking: Async/await throughout
• Disposal tests pass: All IDisposable objects properly cleaned up

Tools Summary

Historical Performance Improvements

v1.0.84 → v1.0.88 (67-73% faster):

• Added --entropy-thold, --no-fallback, optimal threads (40% faster)
• Upgraded whisper.cpp v1.6.0 → v1.7.6 (20-40% faster)
• Added --flash-attn (7-12% faster)
• Q8_0 quantization (same speed, 45% smaller)

Target: Maintain sub-800ms transcription for tiny model