cc: Improve texture per second calculation and overhead

cc/ThrottledTextureUploader.cpp

Index: cc/ThrottledTextureUploader.cpp
diff --git a/cc/ThrottledTextureUploader.cpp b/cc/ThrottledTextureUploader.cpp
index c152598aa648e1586aa9b892e16bd4e53750797d..9c9e50d9ef3a6581c399c53329f8f995efeb7adf 100644
--- a/cc/ThrottledTextureUploader.cpp
+++ b/cc/ThrottledTextureUploader.cpp
@@ -15,7 +15,8 @@
 namespace {
 
 // How many previous uploads to use when predicting future throughput.
-static const size_t uploadHistorySize = 100;
+static const size_t uploadHistorySizeMax = 1000;
+static const size_t uploadHistorySizeInitial = 100;
 
 // Global estimated number of textures per second to maintain estimates across
 // subsequent instances of ThrottledTextureUploader.
@@ -87,7 +88,8 @@ bool ThrottledTextureUploader::Query::isNonBlocking()
 
 ThrottledTextureUploader::ThrottledTextureUploader(WebKit::WebGraphicsContext3D* context)
     : m_context(context)
-    , m_texturesPerSecondHistory(uploadHistorySize, estimatedTexturesPerSecondGlobal)
+    , m_texturesPerSecondHistory(uploadHistorySizeInitial,
+                                 estimatedTexturesPerSecondGlobal)
     , m_numBlockingTextureUploads(0)
 {
 }
@@ -120,15 +122,12 @@ double ThrottledTextureUploader::estimatedTexturesPerSecond()
 {
     processQueries();
 
-    // The history should never be empty because we initialize all elements with an estimate.
-    ASSERT(m_texturesPerSecondHistory.size() == uploadHistorySize);
-
-    // Sort the history and use the median as our estimate.
+    // Sort the history and use the 3/4 median as our optimistic estimate.
     std::vector<double> sortedHistory(m_texturesPerSecondHistory.begin(),
                                       m_texturesPerSecondHistory.end());
     std::sort(sortedHistory.begin(), sortedHistory.end());

[reveman, 2012/10/11 17:59:46]

with the history now relatively large, does it makes sense to do something a bit
smarter than sorting every time estimatedTexturesPerSecond() is called? seems
like a balanced binary tree is just what we need here?

 
-    estimatedTexturesPerSecondGlobal = sortedHistory[sortedHistory.size() * 2 / 3];
+    estimatedTexturesPerSecondGlobal = sortedHistory[sortedHistory.size() * 3 / 4];
     TRACE_COUNTER1("cc", "estimatedTexturesPerSecond", estimatedTexturesPerSecondGlobal);
     return estimatedTexturesPerSecondGlobal;
 }
@@ -178,7 +177,8 @@ void ThrottledTextureUploader::processQueries()
 
         // Remove the oldest values from our history and insert the new one
         double texturesPerSecond = 1.0 / (usElapsed * 1e-6);
-        m_texturesPerSecondHistory.pop_back();
+        if (m_texturesPerSecondHistory.size() >= uploadHistorySizeMax)
+            m_texturesPerSecondHistory.pop_back();
         m_texturesPerSecondHistory.push_front(texturesPerSecond);
 
         m_availableQueries.append(m_pendingQueries.takeFirst());