audio: prevent larger than required sleeps - DO NOT MERGE

b/17962037

From: Haynes Mathew George <hgeorge@codeaurora.org>
Date: Wed, 26 Mar 2014 16:18:42 -0700
Subject: [PATCH] AudioTrack: prevent larger than required sleeps

AudioTrackThread can end up waiting for larger than necessary
time for free space to be available in the cblk. Fix this by
waiting on the cblk futex instead of the (internal) condition variable.

Change-Id: I75bd14cd46f3b75afe0ea8bd9b48d7a2f95f654a

1 files changed, 21 insertions, 1 deletions

diff --git a/media/libmedia/AudioTrack.cpp b/media/libmedia/AudioTrack.cpp
index e290627..4cc50cc 100644
--- a/media/libmedia/AudioTrack.cpp
+++ b/media/libmedia/AudioTrack.cpp
@@ -18,15 +18,21 @@
 
 //#define LOG_NDEBUG 0
 #define LOG_TAG "AudioTrack"
+#define ATRACE_TAG ATRACE_TAG_AUDIO
 
 #include <sys/resource.h>
 #include <audio_utils/primitives.h>
 #include <binder/IPCThreadState.h>
 #include <media/AudioTrack.h>
 #include <utils/Log.h>
+#include <utils/Trace.h>
 #include <private/media/AudioTrackShared.h>
 #include <media/IAudioFlinger.h>
 
+extern "C" {
+#include "../private/bionic_futex.h"
+}
+
 #define WAIT_PERIOD_MS                  10
 #define WAIT_STREAM_END_TIMEOUT_SEC     120
 
@@ -1606,7 +1612,21 @@ nsecs_t AudioTrack::processAudioBuffer(const sp<AudioTrackThread>& thread)
                 if (ns < 0 || myns < ns) {
                     ns = myns;
                 }
-                return ns;
+                int32_t old = android_atomic_and(~CBLK_FUTEX_WAKE, &mCblk->mFutex);
+                char str[64] = {0};
+                struct timespec ts;
+
+                snprintf(str, sizeof(str), "futex_wait timeout %lld Us", ns/1000LL);
+
+                ATRACE_BEGIN(str);
+                ts.tv_sec = 0;
+                ts.tv_nsec = ns;
+                // wait for max ns allowing server to wake us up if possible
+                int ret = __futex_syscall4(&mCblk->mFutex,
+                                           FUTEX_WAIT,
+                                           old & ~CBLK_FUTEX_WAKE, &ts);
+                ATRACE_END();
+                return 0; //retry immediately as space (possibly) became available
             }
         }