feat: audio stack performance improvements

kernel/src/Drivers/Audio/IntelHda.cpp

@@ -1074,6 +1074,22 @@ namespace Drivers::Audio::IntelHda {
         KernelLogStream(OK, "HDA") << "Stream closed";
     }
 
+    uint32_t GetWriteSpace(int handle) {
+        if (handle != 0 || !g_stream.Active) return 0;
+
+        uint32_t hwPos = g_dmaPos[g_stream.StreamIndex * 2];
+        uint32_t writePos = g_stream.WritePos;
+        uint32_t available;
+        if (writePos >= hwPos) {
+            available = TOTAL_BUFFER_SIZE - (writePos - hwPos);
+        } else {
+            available = hwPos - writePos;
+        }
+        if (available > 64) available -= 64;
+        else available = 0;
+        return available;
+    }
+
     int Write(int handle, const uint8_t* data, uint32_t size) {
         if (handle != 0 || !g_stream.Active || !data || size == 0)
             return -1;

kernel/src/Drivers/Audio/IntelHda.hpp

@@ -274,6 +274,13 @@ namespace Drivers::Audio::IntelHda {
     // Returns number of bytes written (may be less than requested if buffer full).
     int Write(int handle, const uint8_t* data, uint32_t size);
 
+    // Free bytes in the DMA ring that a caller may write right now.
+    // Returns 0 if the stream is not active. The mixer uses this to size
+    // each pump so it never produces more than HDA can accept (otherwise
+    // surplus mixed data would be silently dropped and the stream readers
+    // would still advance, scrambling playback).
+    uint32_t GetWriteSpace(int handle);
+
     // Control commands
     constexpr int AUDIO_CTL_SET_VOLUME = 0;   // value: 0-100
     constexpr int AUDIO_CTL_GET_VOLUME = 1;

kernel/src/Drivers/Audio/Mixer.cpp

@@ -164,9 +164,16 @@ namespace Drivers::Audio::Mixer {
     static void Pump() {
         if (!g_hdaOpened) return;
 
-        // Ask IntelHda how much room there is. The driver clamps writes to free
-        // space, so we feed it a generous buffer and let it consume what it can.
-        uint32_t frames = MAX_PUMP_FRAMES;
+        // Produce only as many frames as the HDA DMA ring has room for right
+        // now. Producing more would mean the surplus is silently dropped by
+        // IntelHda::Write while the per-stream resamplers had already
+        // advanced — that's what scrambles speech into a sequence of
+        // unrelated chunks. Clamp to MAX_PUMP_FRAMES so the scratch buffers
+        // are bounded.
+        uint32_t freeBytes = IntelHda::GetWriteSpace(g_hdaHandle);
+        uint32_t frames = freeBytes / 4;
+        if (frames == 0) return;
+        if (frames > MAX_PUMP_FRAMES) frames = MAX_PUMP_FRAMES;
 
         // Always write to HDA, even when no streams are active, so the
         // hardware ring stays filled with silence instead of looping the
@@ -448,15 +455,26 @@ namespace Drivers::Audio::Mixer {
     void SetMasterVolume(int percent) {
         if (percent < 0) percent = 0;
         if (percent > 100) percent = 100;
+
+        // Take the mixer lock just long enough to update software state and
+        // capture a snapshot for the HW write. The IntelHda codec command
+        // path busy-waits on the RIRB for a few hundred microseconds, so
+        // doing it inside the lock would freeze interrupts (BCIS, scheduler,
+        // input) for the whole duration of every drag tick — visible as
+        // slider lag.
         g_lock.Acquire();
         bool changed = (g_masterVolume != percent);
         g_masterVolume = percent;
-        if (g_hdaOpened) {
-            IntelHda::Control(g_hdaHandle, IntelHda::AUDIO_CTL_SET_VOLUME,
-                              g_masterMute ? 0 : g_masterVolume);
-        }
+        int curVol = g_masterVolume;
+        bool curMute = g_masterMute;
+        bool hdaOpen = g_hdaOpened;
         if (changed) BumpSerialLocked();
         g_lock.Release();
+
+        if (changed && hdaOpen) {
+            IntelHda::Control(g_hdaHandle, IntelHda::AUDIO_CTL_SET_VOLUME,
+                              curMute ? 0 : curVol);
+        }
         if (changed) Sched::WakeObjectWaiters((void*)&g_serial);
     }
 
@@ -468,12 +486,16 @@ namespace Drivers::Audio::Mixer {
         g_lock.Acquire();
         bool changed = (g_masterMute != muted);
         g_masterMute = muted;
-        if (g_hdaOpened) {
-            IntelHda::Control(g_hdaHandle, IntelHda::AUDIO_CTL_SET_VOLUME,
-                              g_masterMute ? 0 : g_masterVolume);
-        }
+        int curVol = g_masterVolume;
+        bool curMute = g_masterMute;
+        bool hdaOpen = g_hdaOpened;
         if (changed) BumpSerialLocked();
         g_lock.Release();
+
+        if (changed && hdaOpen) {
+            IntelHda::Control(g_hdaHandle, IntelHda::AUDIO_CTL_SET_VOLUME,
+                              curMute ? 0 : curVol);
+        }
         if (changed) Sched::WakeObjectWaiters((void*)&g_serial);
     }
 

programs/src/audio/main.cpp

@@ -180,6 +180,7 @@ static void refresh_master() {
 static void apply_master_volume(int v) {
     if (v < 0) v = 0;
     if (v > 100) v = 100;
+    if (v == g_master_vol) return;   // No change → skip syscall + HW codec hit.
     g_master_vol = v;
     montauk::audio_set_master_volume(v);
 }
@@ -198,6 +199,7 @@ static void apply_stream_volume(int idx, int v) {
     if (idx < 0 || idx >= g_stream_count) return;
     if (v < 0) v = 0;
     if (v > 100) v = 100;
+    if ((uint8_t)v == g_streams[idx].volume) return;
     g_streams[idx].volume = (uint8_t)v;
     montauk::audio_set_volume(g_streams[idx].handle, v);
 }
@@ -433,13 +435,16 @@ extern "C" void _start() {
 
         // Event-driven sync: the kernel bumps a mixer serial on every state
         // change. Reading it is one cheap syscall; we only re-snapshot the
-        // full mixer state when the serial has actually moved. The master
-        // value is left alone while the user is dragging the master slider
-        // so a mid-drag wakeup can't snap the knob to the kernel value.
+        // full mixer state when the serial has actually moved. Only redraw
+        // when the snapshot differs from what we already show, otherwise
+        // self-driven bumps (e.g. the user dragging our own slider) would
+        // cause a redraw on every drag tick.
         uint64_t now_serial = montauk::audio_wait(g_mixer_serial, 0);
         if (now_serial != g_mixer_serial) {
             g_mixer_serial = now_serial;
 
+            // Master: only refresh when we're not dragging master ourselves,
+            // otherwise a wake mid-drag could snap our knob to the kernel.
             if (g_drag_target != -1) {
                 int prev_vol = g_master_vol;
                 bool prev_muted = g_master_muted;
@@ -448,8 +453,29 @@ extern "C" void _start() {
                     redraw = true;
             }
 
+            // Per-stream: diff before redrawing so dragging the master slider
+            // (which bumps the serial) doesn't trigger redundant repaints.
+            int prev_count = g_stream_count;
+            uint8_t prev_vols[8] = {0};
+            uint8_t prev_mutes[8] = {0};
+            int prev_handles[8] = {0};
+            for (int i = 0; i < prev_count && i < 8; i++) {
+                prev_vols[i]    = g_streams[i].volume;
+                prev_mutes[i]   = g_streams[i].muted;
+                prev_handles[i] = g_streams[i].handle;
+            }
             refresh_streams();
-            redraw = true;
+            if (g_stream_count != prev_count) {
+                redraw = true;
+            } else {
+                for (int i = 0; i < g_stream_count; i++) {
+                    if (g_streams[i].handle != prev_handles[i] ||
+                        g_streams[i].volume != prev_vols[i] ||
+                        g_streams[i].muted != prev_mutes[i]) {
+                        redraw = true; break;
+                    }
+                }
+            }
         }
 
         if (r < 0) break;