feat(audio): add subprocess pre-warming to reduce activation latency

implement batched metrics updates to reduce atomic operations
optimize thread locking for high-throughput scenarios only

internal/audio/api.go

@@ -84,3 +84,21 @@ func GetAudioInputSupervisor() *AudioInputSupervisor {
 	}
 	return (*AudioInputSupervisor)(ptr)
 }
+
+// PrewarmAudioInputSubprocess starts an audio input subprocess in advance to reduce activation latency
+func PrewarmAudioInputSubprocess() error {
+	supervisor := GetAudioInputSupervisor()
+	if supervisor == nil {
+		return nil // No supervisor available, skip prewarming
+	}
+	return supervisor.PrewarmSubprocess()
+}
+
+// IsAudioInputSubprocessPrewarmed returns whether an audio input subprocess is prewarmed and ready
+func IsAudioInputSubprocessPrewarmed() bool {
+	supervisor := GetAudioInputSupervisor()
+	if supervisor == nil {
+		return false
+	}
+	return supervisor.IsPrewarmed()
+}

internal/audio/audio.go

@@ -355,30 +355,94 @@ func GetAudioMetrics() AudioMetrics {
 	}
 }
 
-// RecordFrameReceived increments the frames received counter with simplified tracking
+// Batched metrics to reduce atomic operations frequency
+var (
+	batchedFramesReceived  int64
+	batchedBytesProcessed  int64
+	batchedFramesDropped   int64
+	batchedConnectionDrops int64
+	batchCounter           int64
+	lastFlushTime          int64 // Unix timestamp in nanoseconds
+)
+
+const (
+	// Batch size for metrics updates (reduce atomic ops by 10x)
+	metricsFlushInterval = 10
+	// Force flush every 100ms to ensure metrics freshness
+	metricsForceFlushNanos = 100 * 1000 * 1000 // 100ms in nanoseconds
+)
+
+// RecordFrameReceived increments the frames received counter with batched updates
 func RecordFrameReceived(bytes int) {
-	// Direct atomic updates to avoid sampling complexity in critical path
+	// Use local batching to reduce atomic operations frequency
-	atomic.AddInt64(&metrics.FramesReceived, 1)
+	atomic.AddInt64(&batchedFramesReceived, 1)
-	atomic.AddInt64(&metrics.BytesProcessed, int64(bytes))
+	atomic.AddInt64(&batchedBytesProcessed, int64(bytes))
 
-	// Always update timestamp for accurate last frame tracking
+	// Update timestamp immediately for accurate tracking
 	metrics.LastFrameTime = time.Now()
+
+	// Check if we should flush batched metrics
+	if atomic.AddInt64(&batchCounter, 1)%metricsFlushInterval == 0 {
+		flushBatchedMetrics()
+	} else {
+		// Force flush if too much time has passed
+		now := time.Now().UnixNano()
+		lastFlush := atomic.LoadInt64(&lastFlushTime)
+		if now-lastFlush > metricsForceFlushNanos {
+			flushBatchedMetrics()
+		}
+	}
 }
 
-// RecordFrameDropped increments the frames dropped counter with simplified tracking
+// RecordFrameDropped increments the frames dropped counter with batched updates
 func RecordFrameDropped() {
-	// Direct atomic update to avoid sampling complexity in critical path
+	// Use local batching to reduce atomic operations frequency
-	atomic.AddInt64(&metrics.FramesDropped, 1)
+	atomic.AddInt64(&batchedFramesDropped, 1)
+
+	// Check if we should flush batched metrics
+	if atomic.AddInt64(&batchCounter, 1)%metricsFlushInterval == 0 {
+		flushBatchedMetrics()
+	}
 }
 
-// RecordConnectionDrop increments the connection drops counter with simplified tracking
+// RecordConnectionDrop increments the connection drops counter with batched updates
 func RecordConnectionDrop() {
-	// Direct atomic update to avoid sampling complexity in critical path
+	// Use local batching to reduce atomic operations frequency
-	atomic.AddInt64(&metrics.ConnectionDrops, 1)
+	atomic.AddInt64(&batchedConnectionDrops, 1)
+
+	// Check if we should flush batched metrics
+	if atomic.AddInt64(&batchCounter, 1)%metricsFlushInterval == 0 {
+		flushBatchedMetrics()
+	}
 }
 
-// FlushPendingMetrics is now a no-op since we use direct atomic updates
+// flushBatchedMetrics flushes accumulated metrics to the main counters
-func FlushPendingMetrics() {
+func flushBatchedMetrics() {
-	// No-op: metrics are now updated directly without local buffering
+	// Atomically move batched metrics to main metrics
-	// This function is kept for API compatibility
+	framesReceived := atomic.SwapInt64(&batchedFramesReceived, 0)
+	bytesProcessed := atomic.SwapInt64(&batchedBytesProcessed, 0)
+	framesDropped := atomic.SwapInt64(&batchedFramesDropped, 0)
+	connectionDrops := atomic.SwapInt64(&batchedConnectionDrops, 0)
+
+	// Update main metrics if we have any batched data
+	if framesReceived > 0 {
+		atomic.AddInt64(&metrics.FramesReceived, framesReceived)
+	}
+	if bytesProcessed > 0 {
+		atomic.AddInt64(&metrics.BytesProcessed, bytesProcessed)
+	}
+	if framesDropped > 0 {
+		atomic.AddInt64(&metrics.FramesDropped, framesDropped)
+	}
+	if connectionDrops > 0 {
+		atomic.AddInt64(&metrics.ConnectionDrops, connectionDrops)
+	}
+
+	// Update last flush time
+	atomic.StoreInt64(&lastFlushTime, time.Now().UnixNano())
+}
+
+// FlushPendingMetrics forces a flush of all batched metrics
+func FlushPendingMetrics() {
+	flushBatchedMetrics()
 }

internal/audio/batch_audio.go

@@ -434,7 +434,7 @@ func (bap *BatchAudioProcessor) processBatchRead(batch []batchReadRequest) {
 		// Skip priority setting for better performance - audio threads already have good priority
 	}
 
-	// Update stats efficiently
+	// Batch stats updates to reduce atomic operations (update once per batch instead of per frame)
 	atomic.AddInt64(&bap.stats.BatchedReads, 1)
 	atomic.AddInt64(&bap.stats.BatchedFrames, int64(batchSize))
 	if batchSize > 1 {
@@ -461,6 +461,7 @@ func (bap *BatchAudioProcessor) processBatchRead(batch []batchReadRequest) {
 		bap.stats.OSThreadPinTime += time.Since(start)
 	}
 
+	// Update timestamp only once per batch instead of per frame
 	bap.stats.LastBatchTime = time.Now()
 }
 

internal/audio/config_constants.go

@@ -902,6 +902,12 @@ type AudioConfigConstants struct {
 	// Default 200ms provides reasonable wait time for microphone access.
 	MicContentionTimeout time.Duration // 200ms contention timeout
 
+	// Subprocess Pre-warming Configuration
+	// Used in: input_supervisor.go for reducing microphone activation latency
+	// Impact: Pre-warms audio input subprocess during startup to eliminate cold start delay
+	// Default true enables pre-warming for optimal user experience
+	EnableSubprocessPrewarming bool // Enable subprocess pre-warming (default: true)
+
 	// Priority Scheduler Configuration - Settings for process priority management
 	// Used in: priority_scheduler.go for system priority control
 	// Impact: Controls valid range for process priority adjustments
@@ -2343,6 +2349,9 @@ func DefaultAudioConfig() *AudioConfigConstants {
 		// Microphone Contention Configuration
 		MicContentionTimeout: 200 * time.Millisecond,
 
+		// Subprocess Pre-warming Configuration
+		EnableSubprocessPrewarming: true,
+
 		// Priority Scheduler Configuration
 		MinNiceValue: -20,
 		MaxNiceValue: 19,

internal/audio/input_ipc.go

@@ -1010,12 +1010,19 @@ func (ais *AudioInputServer) startProcessorGoroutine() {
 
 	// Create a processor task that will run in the goroutine pool
 	processorTask := func() {
+		// Only lock OS thread and set priority for high-load scenarios
+		// This reduces interference with input processing threads
+		config := GetConfig()
+		useThreadOptimizations := config.MaxAudioProcessorWorkers > 8
+
+		if useThreadOptimizations {
 			runtime.LockOSThread()
 			defer runtime.UnlockOSThread()
 
-		// Set high priority for audio processing - skip logging in hotpath
+			// Set priority only when necessary to reduce scheduler interference
 			_ = SetAudioThreadPriority()
 			defer func() { _ = ResetThreadPriority() }()
+		}
 
 		// Create logger for this goroutine
 		logger := logging.GetDefaultLogger().With().Str("component", AudioInputServerComponent).Logger()
@@ -1023,8 +1030,8 @@ func (ais *AudioInputServer) startProcessorGoroutine() {
 		// Enhanced error tracking for processing
 		var processingErrors int
 		var lastProcessingError time.Time
-		maxProcessingErrors := GetConfig().MaxConsecutiveErrors
+		maxProcessingErrors := config.MaxConsecutiveErrors
-		errorResetWindow := GetConfig().RestartWindow
+		errorResetWindow := config.RestartWindow
 
 		defer ais.wg.Done()
 		for {
@@ -1127,11 +1134,18 @@ func (ais *AudioInputServer) startMonitorGoroutine() {
 
 	// Create a monitor task that will run in the goroutine pool
 	monitorTask := func() {
+		// Monitor goroutine doesn't need thread locking for most scenarios
+		// Only use thread optimizations for high-throughput scenarios
+		config := GetConfig()
+		useThreadOptimizations := config.MaxAudioProcessorWorkers > 8
+
+		logger := logging.GetDefaultLogger().With().Str("component", AudioInputClientComponent).Logger()
+
+		if useThreadOptimizations {
 			runtime.LockOSThread()
 			defer runtime.UnlockOSThread()
 
-		// Set I/O priority for monitoring
+			// Set I/O priority for monitoring only when needed
-		logger := logging.GetDefaultLogger().With().Str("component", AudioInputClientComponent).Logger()
 			if err := SetAudioIOThreadPriority(); err != nil {
 				logger.Warn().Err(err).Msg("Failed to set audio I/O priority")
 			}
@@ -1140,6 +1154,7 @@ func (ais *AudioInputServer) startMonitorGoroutine() {
 					logger.Warn().Err(err).Msg("Failed to reset thread priority")
 				}
 			}()
+		}
 
 		defer ais.wg.Done()
 		ticker := time.NewTicker(GetConfig().DefaultTickerInterval)

internal/audio/input_supervisor.go

@@ -21,6 +21,10 @@ type AudioInputSupervisor struct {
 
 	// Environment variables for OPUS configuration
 	opusEnv []string
+
+	// Pre-warming state
+	prewarmed   bool
+	prewarmTime time.Time
 }
 
 // NewAudioInputSupervisor creates a new audio input supervisor
@@ -48,6 +52,73 @@ func (ais *AudioInputSupervisor) SetOpusConfig(bitrate, complexity, vbr, signalT
 	}
 }
 
+// PrewarmSubprocess starts a subprocess in advance to reduce activation latency
+func (ais *AudioInputSupervisor) PrewarmSubprocess() error {
+	ais.mutex.Lock()
+	defer ais.mutex.Unlock()
+
+	// Don't prewarm if already running or prewarmed
+	if ais.IsRunning() || ais.prewarmed {
+		return nil
+	}
+
+	// Check for existing audio input server process first
+	if existingPID, err := ais.findExistingAudioInputProcess(); err == nil {
+		ais.logger.Info().Int("existing_pid", existingPID).Msg("Found existing audio input server process for prewarming")
+		ais.prewarmed = true
+		ais.prewarmTime = time.Now()
+		return nil
+	}
+
+	// Create context for subprocess management
+	ais.createContext()
+
+	// Get current executable path
+	execPath, err := os.Executable()
+	if err != nil {
+		return fmt.Errorf("failed to get executable path: %w", err)
+	}
+
+	// Build command arguments (only subprocess flag)
+	args := []string{"--audio-input-server"}
+
+	// Create command for audio input server subprocess
+	cmd := exec.CommandContext(ais.ctx, execPath, args...)
+
+	// Set environment variables for IPC and OPUS configuration
+	env := append(os.Environ(), "JETKVM_AUDIO_INPUT_IPC=true") // Enable IPC mode
+	env = append(env, ais.opusEnv...)                          // Add OPUS configuration
+	cmd.Env = env
+
+	// Set process group to allow clean termination
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Setpgid: true,
+	}
+
+	ais.cmd = cmd
+
+	// Start the subprocess
+	err = cmd.Start()
+	if err != nil {
+		ais.cancelContext()
+		return fmt.Errorf("failed to prewarm audio input server process: %w", err)
+	}
+
+	ais.logger.Info().Int("pid", cmd.Process.Pid).Strs("args", args).Strs("opus_env", ais.opusEnv).Msg("Audio input server subprocess prewarmed")
+
+	// Add process to monitoring
+	ais.processMonitor.AddProcess(cmd.Process.Pid, "audio-input-server")
+
+	// Monitor the subprocess in a goroutine
+	go ais.monitorSubprocess()
+
+	// Mark as prewarmed
+	ais.prewarmed = true
+	ais.prewarmTime = time.Now()
+
+	return nil
+}
+
 // Start starts the audio input server subprocess
 func (ais *AudioInputSupervisor) Start() error {
 	ais.mutex.Lock()
@@ -60,6 +131,16 @@ func (ais *AudioInputSupervisor) Start() error {
 		return fmt.Errorf("audio input supervisor already running")
 	}
 
+	// Use prewarmed subprocess if available
+	if ais.prewarmed && ais.cmd != nil && ais.cmd.Process != nil {
+		ais.logger.Info().Int("pid", ais.cmd.Process.Pid).Dur("prewarm_age", time.Since(ais.prewarmTime)).Msg("Using prewarmed audio input server subprocess")
+		ais.setRunning(true)
+		ais.prewarmed = false // Reset prewarmed state
+		// Connect client to the server
+		go ais.connectClient()
+		return nil
+	}
+
 	// Check for existing audio input server process
 	if existingPID, err := ais.findExistingAudioInputProcess(); err == nil {
 		ais.logger.Info().Int("existing_pid", existingPID).Msg("Found existing audio input server process, connecting to it")
@@ -120,11 +201,31 @@ func (ais *AudioInputSupervisor) Start() error {
 	return nil
 }
 
+// IsPrewarmed returns whether a subprocess is prewarmed and ready
+func (ais *AudioInputSupervisor) IsPrewarmed() bool {
+	ais.mutex.RLock()
+	defer ais.mutex.RUnlock()
+	return ais.prewarmed
+}
+
+// GetPrewarmAge returns how long ago the subprocess was prewarmed
+func (ais *AudioInputSupervisor) GetPrewarmAge() time.Duration {
+	ais.mutex.RLock()
+	defer ais.mutex.RUnlock()
+	if !ais.prewarmed {
+		return 0
+	}
+	return time.Since(ais.prewarmTime)
+}
+
 // Stop stops the audio input server subprocess
 func (ais *AudioInputSupervisor) Stop() {
 	ais.mutex.Lock()
 	defer ais.mutex.Unlock()
 
+	// Reset prewarmed state
+	ais.prewarmed = false
+
 	if !ais.IsRunning() {
 		return
 	}

internal/audio/output_streaming.go

@@ -135,9 +135,14 @@ func (s *AudioOutputStreamer) Stop() {
 func (s *AudioOutputStreamer) streamLoop() {
 	defer s.wg.Done()
 
-	// Pin goroutine to OS thread for consistent performance
+	// Only pin to OS thread for high-throughput scenarios to reduce scheduler interference
+	config := GetConfig()
+	useThreadOptimizations := config.MaxAudioProcessorWorkers > 8
+
+	if useThreadOptimizations {
 		runtime.LockOSThread()
 		defer runtime.UnlockOSThread()
+	}
 
 	// Adaptive timing for frame reading
 	frameInterval := time.Duration(GetConfig().OutputStreamingFrameIntervalMS) * time.Millisecond // 50 FPS base rate
@@ -198,6 +203,11 @@ func (s *AudioOutputStreamer) streamLoop() {
 func (s *AudioOutputStreamer) processingLoop() {
 	defer s.wg.Done()
 
+	// Only use thread optimizations for high-throughput scenarios
+	config := GetConfig()
+	useThreadOptimizations := config.MaxAudioProcessorWorkers > 8
+
+	if useThreadOptimizations {
 		// Pin goroutine to OS thread for consistent performance
 		runtime.LockOSThread()
 		defer runtime.UnlockOSThread()
@@ -217,6 +227,7 @@ func (s *AudioOutputStreamer) processingLoop() {
 				}
 			}
 		}()
+	}
 
 	for frameData := range s.processingChan {
 		// Process frame and return buffer to pool after processing

main.go

@@ -68,6 +68,17 @@ func startAudioSubprocess() error {
 		config.AudioQualityLowOpusDTX,
 	)
 
+	// Pre-warm audio input subprocess to reduce activation latency (if enabled)
+	if config.EnableSubprocessPrewarming {
+		if err := audio.PrewarmAudioInputSubprocess(); err != nil {
+			logger.Warn().Err(err).Msg("failed to pre-warm audio input subprocess")
+		} else {
+			logger.Info().Msg("audio input subprocess pre-warmed successfully")
+		}
+	} else {
+		logger.Info().Msg("audio input subprocess pre-warming disabled by configuration")
+	}
+
 	// Note: Audio input supervisor is NOT started here - it will be started on-demand
 	// when the user activates microphone input through the UI