Reduce the number of flushes while using glQueries.

gpu/command_buffer/client/query_tracker.cc

Index: gpu/command_buffer/client/query_tracker.cc
diff --git a/gpu/command_buffer/client/query_tracker.cc b/gpu/command_buffer/client/query_tracker.cc
index 5ac89e07e0f5ca472d767f99b86815ef2984be5f..c5014904bc7172e0b8474ca34c46821e99e1555a 100644
--- a/gpu/command_buffer/client/query_tracker.cc
+++ b/gpu/command_buffer/client/query_tracker.cc
@@ -93,7 +93,7 @@ QueryTracker::Query::Query(GLuint id, GLenum target,
       state_(kUninitialized),
       submit_count_(0),
       token_(0),
-      flushed_(false),
+      last_flush_(0),
       client_begin_time_us_(0),
       result_(0) {
     }
@@ -140,6 +140,7 @@ void QueryTracker::Query::End(GLES2Implementation* gl) {
       }
     }
   }
+  last_flush_ = gl->helper()->flush_generation();
   gl->helper()->EndQueryEXT(target(), submit_count());
   MarkAsPending(gl->helper()->InsertToken());
 }
@@ -168,13 +169,10 @@ bool QueryTracker::Query::CheckResultsAvailable(
       }
       state_ = kComplete;
     } else {
-      if (!flushed_) {
-        // TODO(gman): We could reduce the number of flushes by having a
-        // flush count, recording that count at the time we insert the
-        // EndQuery command and then only flushing here if we've have not
-        // passed that count yet.
-        flushed_ = true;
+      uint32 flush_generation = helper->flush_generation();
+      if (!(flush_generation>last_flush_)) {
         helper->Flush();
+        ++last_flush_;

[Zhenyao Mo, 2014/04/08 18:55:40]

This should be last_flush_ = helper->flush_generation() instead.

[rptr, 2014/04/08 20:58:49]

Yes I agree. Better to set/get flush_count from a common place.

       } else {
         // Insert no-ops so that eventually the GPU process will see more work.
         helper->Noop(1);