Bug 1085186. Don't readahead more than 30s of media data per resource…

… on mobile/B2G. r=cpearce

b2g/app/b2g.js

@@ -319,6 +319,11 @@ pref("dom.indexedDB.warningQuota", 5);
 pref("media.preload.default", 1); // default to preload none
 pref("media.preload.auto", 2);    // preload metadata if preload=auto
 pref("media.cache_size", 4096);    // 4MB media cache
+// Try to save battery by not resuming reading from a connection until we fall
+// below 10s of buffered data.
+pref("media.cache_resume_threshold", 10);
+pref("media.cache_readahead_limit", 30);
+
 #ifdef MOZ_FMP4
 // Enable/Disable Gonk Decoder Module
 pref("media.fragmented-mp4.gonk.enabled", false);

dom/media/MediaCache.cpp

@@ -56,10 +56,6 @@ static const uint32_t REPLAY_PENALTY_FACTOR = 3;
 // can.
 static const uint32_t FREE_BLOCK_SCAN_LIMIT = 16;
 
-// Try to save power by not resuming paused reads if the stream won't need new
-// data within this time interval in the future
-static const uint32_t CACHE_POWERSAVE_WAKEUP_LOW_THRESHOLD_MS = 10000;
-
 #ifdef DEBUG
 // Turn this on to do very expensive cache state validation
 // #define DEBUG_VERIFY_CACHE
@@ -1164,6 +1160,9 @@ MediaCache::Update()
       }
     }
 
+    int32_t resumeThreshold = Preferences::GetInt("media.cache_resume_threshold", 10);
+    int32_t readaheadLimit = Preferences::GetInt("media.cache_readahead_limit", 30);
+
     for (uint32_t i = 0; i < mStreams.Length(); ++i) {
       actions.AppendElement(NONE);
 
@@ -1245,10 +1244,14 @@ MediaCache::Update()
         TimeDuration predictedNewDataUse = PredictNextUseForIncomingData(stream);
 
         if (stream->mCacheSuspended &&
-            predictedNewDataUse.ToMilliseconds() > CACHE_POWERSAVE_WAKEUP_LOW_THRESHOLD_MS) {
+            predictedNewDataUse.ToSeconds() > resumeThreshold) {
           // Don't need data for a while, so don't bother waking up the stream
           CACHE_LOG(PR_LOG_DEBUG, ("Stream %p avoiding wakeup since more data is not needed", stream));
           enableReading = false;
+        } else if (predictedNewDataUse.ToSeconds() > readaheadLimit) {
+          // Don't read ahead more than this much
+          CACHE_LOG(PR_LOG_DEBUG, ("Stream %p throttling to avoid reading ahead too far", stream));
+          enableReading = false;
         } else if (freeBlockCount > 0) {
           // Free blocks in the cache, so keep reading
           CACHE_LOG(PR_LOG_DEBUG, ("Stream %p reading since there are free blocks", stream));

mobile/android/app/mobile.js

@@ -552,6 +552,11 @@ pref("dom.indexedDB.warningQuota", 5);
 // prevent video elements from preloading too much data
 pref("media.preload.default", 1); // default to preload none
 pref("media.preload.auto", 2);    // preload metadata if preload=auto
+pref("media.cache_size", 32768);    // 32MB media cache
+// Try to save battery by not resuming reading from a connection until we fall
+// below 10s of buffered data.
+pref("media.cache_resume_threshold", 10);
+pref("media.cache_readahead_limit", 30);
 
 // Number of video frames we buffer while decoding video.
 // On Android this is decided by a similar value which varies for

modules/libpref/init/all.js

@@ -233,6 +233,13 @@ pref("print.shrink-to-fit.scale-limit-percent", 20);
 
 // Media cache size in kilobytes
 pref("media.cache_size", 512000);
+// When a network connection is suspended, don't resume it until the
+// amount of buffered data falls below this threshold (in seconds).
+pref("media.cache_resume_threshold", 999999);
+// Stop reading ahead when our buffered data is this many seconds ahead
+// of the current playback position. This limit can stop us from using arbitrary
+// amounts of network bandwidth prefetching huge videos.
+pref("media.cache_readahead_limit", 999999);
 
 // Master HTML5 media volume scale.
 pref("media.volume_scale", "1.0");