Remove timing jitter during startup of audio

This fixes a regression introduced recently, that increased timing jitter
during the startup of the FastMixer and AudioTrack callback threads.

The regression was to make requestPriority() asynchronous as a way to
avoid an apparent priority inversion in system_server.  This means that
the target thread could run briefly with the initial priority, before
the new priority takes effect.

This change removes the startup jitter for FastMixer, by making the
requestPriority() synchronous again for that case.  It doesn't matter
that this restores the priority inversion involving normal mixer thread,
because it happens during startup of both threads.

The change also removes the startup jitter for the AudioTrack callback
thread, by having the target thread check whether the requestPriority()
has completed yet.  If not, the target thread blocks with a timeout
until the priority boost finishes.

Finally, we now log an error message if the expected priority boost
doesn't happen.

Bug: 8698989
Change-Id: Id590e9a274b70ec1ba85b44a585ee37a22e41cbc

1 files changed, 21 insertions, 0 deletions

diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index 1bd839f..7eeb4f8 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -893,9 +893,11 @@ status_t AudioTrack::createTrack_l(
         ALOGW("Requested frameCount %u but received frameCount %u", frameCount, temp);
     }
     frameCount = temp;
+    mAwaitBoost = false;
     if (flags & AUDIO_OUTPUT_FLAG_FAST) {
         if (trackFlags & IAudioFlinger::TRACK_FAST) {
             ALOGV("AUDIO_OUTPUT_FLAG_FAST successful; frameCount %u", frameCount);
+            mAwaitBoost = true;
         } else {
             ALOGV("AUDIO_OUTPUT_FLAG_FAST denied by server; frameCount %u", frameCount);
             // once denied, do not request again if IAudioTrack is re-created
@@ -1219,6 +1221,25 @@ bool AudioTrack::processAudioBuffer(const sp<AudioTrackThread>& thread)
     size_t writtenSize;
 
     mLock.lock();
+    if (mAwaitBoost) {
+        mAwaitBoost = false;
+        mLock.unlock();
+        static const int32_t kMaxTries = 5;
+        int32_t tryCounter = kMaxTries;
+        uint32_t pollUs = 10000;
+        do {
+            int policy = sched_getscheduler(0);
+            if (policy == SCHED_FIFO || policy == SCHED_RR) {
+                break;
+            }
+            usleep(pollUs);
+            pollUs <<= 1;
+        } while (tryCounter-- > 0);
+        if (tryCounter < 0) {
+            ALOGE("did not receive expected priority boost on time");
+        }
+        return true;
+    }
     // acquire a strong reference on the IMemory and IAudioTrack so that they cannot be destroyed
     // while we are accessing the cblk
     sp<IAudioTrack> audioTrack = mAudioTrack;