With latch support and higher level frame throttling, we no longer need to limit SwapBuffers calls by using glSet/TestFenceNV in GpuScheduler.

BUG=79940
TEST=open page with CSS 3D transform animation; open about:gpu and start tracing; verify that between frames, there are not many short calls to ProcessCommands

Review URL: http://codereview.chromium.org/6873095

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@82197 0039d316-1c4b-4281-b951-d872f2087c98

5 files changed, 11 insertions, 62 deletions

diff --git a/gpu/command_buffer/common/constants.h b/gpu/command_buffer/common/constants.h
index 6ef22aa..ca1d5a8 100644
--- a/gpu/command_buffer/common/constants.h
+++ b/gpu/command_buffer/common/constants.h
@@ -26,14 +26,13 @@ namespace error {
     // This is not an error. It is returned by WaitLatch when it is blocked.
     // When blocked, the context will not reschedule itself until another
     // context executes a SetLatch command.
-    kWaiting,
-
-    // This is not an error. It is returned by commands to mark a position
-    // in the command buffer that should not be issued to the the GL backend
-    // until no more than a fixed number of such positions have already been
-    // issued.
-    kThrottle
+    kWaiting
   };
+
+  // Return true if the given error code is an actual error.
+  inline bool IsError(Error error) {
+    return (error != kNoError && error != kWaiting);
+  }
 }
 
 // Invalid shared memory Id, returned by RegisterSharedMemory in case of
diff --git a/gpu/command_buffer/service/cmd_parser.cc b/gpu/command_buffer/service/cmd_parser.cc
index 199eb05..9ed3fca 100644
--- a/gpu/command_buffer/service/cmd_parser.cc
+++ b/gpu/command_buffer/service/cmd_parser.cc
@@ -59,9 +59,7 @@ error::Error CommandParser::ProcessCommand() {
   // TODO(gman): If you want to log errors this is the best place to catch them.
   //     It seems like we need an official way to turn on a debug mode and
   //     get these errors.
-  if (result != error::kNoError &&
-      result != error::kThrottle &&
-      result != error::kWaiting) {
+  if (error::IsError(result)) {
     ReportError(header.command, result);
   }
 
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index db58132..42f9a2b 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -6341,7 +6341,7 @@ error::Error GLES2DecoderImpl::HandleSwapBuffers(
       if (swap_buffers_callback_.get()) {
         swap_buffers_callback_->Run();
       }
-      return error::kThrottle;
+      return error::kNoError;
     } else {
       ScopedFrameBufferBinder binder(this,
                                      offscreen_target_frame_buffer_->id());
@@ -6363,7 +6363,7 @@ error::Error GLES2DecoderImpl::HandleSwapBuffers(
       if (swap_buffers_callback_.get()) {
         swap_buffers_callback_->Run();
       }
-      return error::kThrottle;
+      return error::kNoError;
     }
   } else {
     if (!context_->SwapBuffers()) {
@@ -6376,14 +6376,7 @@ error::Error GLES2DecoderImpl::HandleSwapBuffers(
     swap_buffers_callback_->Run();
   }
 
-  // Do not throttle SwapBuffers by returning kThrottle. The intent of
-  // throttling the offscreen command buffers to a fixed number of frames
-  // ahead is to prevent them from rendering faster than they can be
-  // presented, not to limit the rate at which we present.
-  //
-  // This does not hold for ANGLE, possibly because all the GL contexts in a
-  // share group are actually one D3D device. Found by trial and error.
-  return IsAngle() ? error::kThrottle : error::kNoError;
+  return error::kNoError;
 }
 
 error::Error GLES2DecoderImpl::HandleSetLatchCHROMIUM(
diff --git a/gpu/command_buffer/service/gpu_scheduler.cc b/gpu/command_buffer/service/gpu_scheduler.cc
index 1ae36c4..1782dec 100644
--- a/gpu/command_buffer/service/gpu_scheduler.cc
+++ b/gpu/command_buffer/service/gpu_scheduler.cc
@@ -13,15 +13,12 @@
 
 using ::base::SharedMemory;
 
-static size_t kNumThrottleFences = 1;
-
 namespace gpu {
 
 GpuScheduler::GpuScheduler(CommandBuffer* command_buffer,
                            gles2::ContextGroup* group)
     : command_buffer_(command_buffer),
       commands_per_update_(100),
-      num_throttle_fences_(0),
 #if defined(OS_MACOSX)
       swap_buffers_count_(0),
       acknowledged_swap_buffers_count_(0),
@@ -38,7 +35,6 @@ GpuScheduler::GpuScheduler(CommandBuffer* command_buffer,
                            int commands_per_update)
     : command_buffer_(command_buffer),
       commands_per_update_(commands_per_update),
-      num_throttle_fences_(0),
 #if defined(OS_MACOSX)
       swap_buffers_count_(0),
       acknowledged_swap_buffers_count_(0),
@@ -66,11 +62,6 @@ bool GpuScheduler::InitializeCommon(
   if (!context->MakeCurrent())
     return false;
 
-  // If the NV_fence extension is present, use fences to defer the issue of
-  // commands once a certain fixed number of frames have been rendered.
-  num_throttle_fences_ =
-      context->HasExtension("GL_NV_fence") ? kNumThrottleFences : 0;
-
   // Do not limit to a certain number of commands before scheduling another
   // update when rendering onscreen.
   if (!context->IsOffscreen())
@@ -153,19 +144,6 @@ void GpuScheduler::ProcessCommands() {
   }
 #endif
 
-  // Defer this command until the fence queue is not full.
-  while (num_throttle_fences_ > 0 &&
-      throttle_fences_.size() >= num_throttle_fences_) {
-    GLuint fence = throttle_fences_.front();
-    if (!glTestFenceNV(fence)) {
-      ScheduleProcessCommands();
-      return;
-    }
-
-    glDeleteFencesNV(1, &fence);
-    throttle_fences_.pop();
-  }
-
   error::Error error = error::kNoError;
   int commands_processed = 0;
   while (commands_processed < commands_per_update_ && !parser_->IsEmpty()) {
@@ -174,23 +152,7 @@ void GpuScheduler::ProcessCommands() {
       break;
     }
 
-    // If the command indicated it should be throttled, insert a new fence into
-    // the fence queue.
-    if (error == error::kThrottle) {
-      if (num_throttle_fences_ > 0 &&
-          throttle_fences_.size() < num_throttle_fences_) {
-        GLuint fence;
-        glGenFencesNV(1, &fence);
-        glSetFenceNV(fence, GL_ALL_COMPLETED_NV);
-        throttle_fences_.push(fence);
-
-        // Neither glTestFenceNV or glSetFenceNV are guaranteed to flush.
-        // Without an explicit flush, the glTestFenceNV loop might never
-        // make progress.
-        glFlush();
-        break;
-      }
-    } else if (error != error::kNoError) {
+    if (error::IsError(error)) {
       command_buffer_->SetParseError(error);
       return;
     }
diff --git a/gpu/command_buffer/service/gpu_scheduler.h b/gpu/command_buffer/service/gpu_scheduler.h
index 36cc009..173e953 100644
--- a/gpu/command_buffer/service/gpu_scheduler.h
+++ b/gpu/command_buffer/service/gpu_scheduler.h
@@ -151,9 +151,6 @@ class GpuScheduler : public CommandBufferEngine {
   scoped_ptr<gles2::GLES2Decoder> decoder_;
   scoped_ptr<CommandParser> parser_;
 
-  size_t num_throttle_fences_;
-  std::queue<unsigned> throttle_fences_;
-
 #if defined(OS_MACOSX)
   scoped_ptr<AcceleratedSurface> surface_;
   uint64 swap_buffers_count_;