Increase kFastTrackMultiplier from 1 to 2

Bug: 11967381
Change-Id: Iedec06280aa745d9df5d661f4916940cede9c191

2 files changed, 14 insertions, 11 deletions

diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index ccd1b49..11b0b89 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -879,7 +879,8 @@ status_t AudioTrack::createTrack_l(
     ALOGV("createTrack_l() output %d afLatency %d", output, afLatency);
 
     // The client's AudioTrack buffer is divided into n parts for purpose of wakeup by server, where
-    //  n = 1   fast track; nBuffering is ignored
+    //  n = 1   fast track with single buffering; nBuffering is ignored
+    //  n = 2   fast track with double buffering
     //  n = 2   normal track, no sample rate conversion
     //  n = 3   normal track, with sample rate conversion
     //          (pessimistic; some non-1:1 conversion ratios don't actually need triple-buffering)
@@ -1019,9 +1020,11 @@ status_t AudioTrack::createTrack_l(
             ALOGV("AUDIO_OUTPUT_FLAG_FAST successful; frameCount %u", frameCount);
             mAwaitBoost = true;
             if (sharedBuffer == 0) {
-                // double-buffering is not required for fast tracks, due to tighter scheduling
-                if (mNotificationFramesAct == 0 || mNotificationFramesAct > frameCount) {
-                    mNotificationFramesAct = frameCount;
+                // Theoretically double-buffering is not required for fast tracks,
+                // due to tighter scheduling.  But in practice, to accommodate kernels with
+                // scheduling jitter, and apps with computation jitter, we use double-buffering.
+                if (mNotificationFramesAct == 0 || mNotificationFramesAct > frameCount/nBuffering) {
+                    mNotificationFramesAct = frameCount/nBuffering;
                 }
             }
         } else {
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index 4f1c01d..3d657b3 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -135,12 +135,12 @@ static const int kPriorityFastMixer = 3;
 
 // IAudioFlinger::createTrack() reports back to client the total size of shared memory area
 // for the track.  The client then sub-divides this into smaller buffers for its use.
-// Currently the client uses double-buffering by default, but doesn't tell us about that.
-// So for now we just assume that client is double-buffered.
-// FIXME It would be better for client to tell AudioFlinger whether it wants double-buffering or
-// N-buffering, so AudioFlinger could allocate the right amount of memory.
+// Currently the client uses N-buffering by default, but doesn't tell us about the value of N.
+// So for now we just assume that client is double-buffered for fast tracks.
+// FIXME It would be better for client to tell AudioFlinger the value of N,
+// so AudioFlinger could allocate the right amount of memory.
 // See the client's minBufCount and mNotificationFramesAct calculations for details.
-static const int kFastTrackMultiplier = 1;
+static const int kFastTrackMultiplier = 2;
 
 // ----------------------------------------------------------------------------
 
@@ -1210,7 +1210,7 @@ sp<AudioFlinger::PlaybackThread::Track> AudioFlinger::PlaybackThread::createTrac
               (
                 (tid != -1) &&
                 ((frameCount == 0) ||
-                (frameCount >= (mFrameCount * kFastTrackMultiplier)))
+                (frameCount >= mFrameCount))
               )
             ) &&
             // PCM data
@@ -4687,7 +4687,7 @@ sp<AudioFlinger::RecordThread::RecordTrack>  AudioFlinger::RecordThread::createR
             (
                 (tid != -1) &&
                 ((frameCount == 0) ||
-                (frameCount >= (mFrameCount * kFastTrackMultiplier)))
+                (frameCount >= mFrameCount))
             ) &&
             // FIXME when record supports non-PCM data, also check for audio_is_linear_pcm(format)
             // mono or stereo