Add audio buffer statistics measurement.

driver.c

@@ -434,6 +434,52 @@ void init_audio(void)
 #ifdef HAVE_DYLIB
    init_dsp_plugin();
 #endif
+
+   g_extern.audio_data.buffer_free_samples_count = 0;
+}
+
+static void compute_audio_buffer_statistics(void)
+{
+   unsigned samples = min(g_extern.audio_data.buffer_free_samples_count, AUDIO_BUFFER_FREE_SAMPLES_COUNT);
+   if (!samples)
+      return;
+
+   uint64_t accum = 0;
+   for (unsigned i = 0; i < samples; i++)
+      accum += g_extern.audio_data.buffer_free_samples[i];
+
+   int avg = accum / samples;
+
+   uint64_t accum_var = 0;
+   for (unsigned i = 0; i < samples; i++)
+   {
+      int diff = avg - g_extern.audio_data.buffer_free_samples[i];
+      accum_var += diff * diff;
+   }
+
+   unsigned stddev = (unsigned)sqrtf((float)accum_var / samples);
+
+   float avg_filled = 1.0f - (float)avg / g_extern.audio_data.driver_buffer_size;
+   float deviation = (float)stddev / g_extern.audio_data.driver_buffer_size;
+
+   unsigned low_water_size = g_extern.audio_data.driver_buffer_size * 3 / 4;
+   unsigned high_water_size = g_extern.audio_data.driver_buffer_size / 4;
+
+   unsigned low_water_count = 0;
+   unsigned high_water_count = 0;
+   for (unsigned i = 0; i < samples; i++)
+   {
+      if (g_extern.audio_data.buffer_free_samples[i] >= low_water_size)
+         low_water_count++;
+      else if (g_extern.audio_data.buffer_free_samples[i] <= high_water_size)
+         high_water_count++;
+   }
+
+   RARCH_LOG("Average audio buffer saturation: %.2f %%, standard deviation (percentage points): %.2f %%.\n",
+         avg_filled * 100.0, deviation * 100.0);
+   RARCH_LOG("Amount of time spent close to underrun: %.2f %%. Close to blocking: %.2f %%.\n",
+         (100.0 * low_water_count) / samples,
+         (100.0 * high_water_count) / samples);
 }
 
 void uninit_audio(void)
@@ -466,6 +512,8 @@ void uninit_audio(void)
 #ifdef HAVE_DYLIB
    deinit_dsp_plugin();
 #endif
+
+   compute_audio_buffer_statistics();
 }
 
 #ifdef HAVE_DYLIB

general.h

@@ -401,6 +401,10 @@ struct global
 
       float volume_db;
       float volume_gain;
+
+#define AUDIO_BUFFER_FREE_SAMPLES_COUNT (8 * 1024)
+      unsigned buffer_free_samples[AUDIO_BUFFER_FREE_SAMPLES_COUNT];
+      uint64_t buffer_free_samples_count;
    } audio_data;
 
    struct

retroarch.c

@@ -182,6 +182,9 @@ static void readjust_audio_input_rate(void)
    //RARCH_LOG_OUTPUT("Audio buffer is %u%% full\n",
    //      (unsigned)(100 - (avail * 100) / g_extern.audio_data.driver_buffer_size));
 
+   unsigned write_index = (g_extern.audio_data.buffer_free_samples_count++) & (AUDIO_BUFFER_FREE_SAMPLES_COUNT - 1);
+   g_extern.audio_data.buffer_free_samples[write_index] = avail;
+
    int half_size = g_extern.audio_data.driver_buffer_size / 2;
    int delta_mid = avail - half_size;
    double direction = (double)delta_mid / half_size;