Add a yield command to the command buffer.

This allows more graceful scheduling so that waiting on the previous frame's swapbuffers doesn't end up being a Finish.

BUG=none
TEST=check in about:gpu and verify that SwapBuffers in the renderer process actually only waits for the previous SwapBuffers in the gpu process.

Review URL: http://codereview.chromium.org/6899037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@82759 0039d316-1c4b-4281-b951-d872f2087c98

9 files changed, 73 insertions, 11 deletions

diff --git a/gpu/command_buffer/client/cmd_buffer_helper.cc b/gpu/command_buffer/client/cmd_buffer_helper.cc
index 3f7d94e..8da55b69 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper.cc
@@ -112,6 +112,11 @@ void CommandBufferHelper::WaitForToken(int32 token) {
   }
 }
 
+void CommandBufferHelper::YieldScheduler() {
+  cmd::YieldScheduler& cmd = GetCmdSpace<cmd::YieldScheduler>();
+  cmd.Init();
+}
+
 // Waits for available entries, basically waiting until get >= put + count + 1.
 // It actually waits for contiguous entries, so it may need to wrap the buffer
 // around, adding a jump. Thus this function may change the value of put_. The
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.h b/gpu/command_buffer/client/cmd_buffer_helper.h
index c28333a..0f41b9b 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.h
+++ b/gpu/command_buffer/client/cmd_buffer_helper.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -82,6 +82,11 @@ class CommandBufferHelper {
   //   the value of the token to wait for.
   void WaitForToken(int32 token);
 
+  // Inserts a yield command, signaling the scheduler that this is a good point
+  // to update the state and schedule other command buffers. This is
+  // particularly useful after inserting a token that will be waited on.
+  void YieldScheduler();
+
   // Waits for a certain amount of space to be available. Returns address
   // of space.
   CommandBufferEntry* GetSpace(uint32 entries);
diff --git a/gpu/command_buffer/client/gles2_implementation.cc b/gpu/command_buffer/client/gles2_implementation.cc
index 86b3bc4..aa94fbb 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -691,6 +691,7 @@ void GLES2Implementation::SwapBuffers() {
   }
   helper_->SwapBuffers();
   swap_buffers_tokens_.push(helper_->InsertToken());
+  helper_->YieldScheduler();
   Flush();
 }
 
diff --git a/gpu/command_buffer/common/cmd_buffer_common.h b/gpu/command_buffer/common/cmd_buffer_common.h
index e8bcd43..80d1e28 100644
--- a/gpu/command_buffer/common/cmd_buffer_common.h
+++ b/gpu/command_buffer/common/cmd_buffer_common.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -157,6 +157,7 @@ namespace cmd {
   OP(SetBucketDataImmediate)        /*  9 */ \
   OP(GetBucketSize)                 /* 10 */ \
   OP(GetBucketData)                 /* 11 */ \
+  OP(YieldScheduler)                /* 12 */ \
 
 // Common commands.
 enum CommandId {
@@ -641,6 +642,32 @@ COMPILE_ASSERT(offsetof(GetBucketData, shared_memory_id) == 16,
 COMPILE_ASSERT(offsetof(GetBucketData, shared_memory_offset) == 20,
                Offsetof_GetBucketData_shared_memory_offset_not_20);
 
+// A Yield command. Hints the scheduler that this is a good point to update the
+// state and schedule other command buffers.
+struct YieldScheduler {
+  typedef YieldScheduler ValueType;
+  static const CommandId kCmdId = kYieldScheduler;
+  static const cmd::ArgFlags kArgFlags = cmd::kFixed;
+
+  void SetHeader() {
+    header.SetCmd<ValueType>();
+  }
+
+  void Init() {
+    SetHeader();
+  }
+  static void* Set(void* cmd) {
+    static_cast<ValueType*>(cmd)->Init();
+    return NextCmdAddress<ValueType>(cmd);
+  }
+
+  CommandHeader header;
+};
+
+COMPILE_ASSERT(sizeof(YieldScheduler) == 4, Sizeof_YieldScheduler_is_not_4);
+COMPILE_ASSERT(offsetof(YieldScheduler, header) == 0,
+               Offsetof_YieldScheduler_header_not_0);
+
 }  // namespace cmd
 
 #pragma pack(pop)
diff --git a/gpu/command_buffer/common/constants.h b/gpu/command_buffer/common/constants.h
index ca1d5a8..3b06cad 100644
--- a/gpu/command_buffer/common/constants.h
+++ b/gpu/command_buffer/common/constants.h
@@ -26,12 +26,23 @@ 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
+    kWaiting,
+
+    // This is not an error either. It just hints the scheduler that it can exit
+    // its loop, update state, and schedule other command buffers.
+    kYield
   };
 
   // Return true if the given error code is an actual error.
   inline bool IsError(Error error) {
-    return (error != kNoError && error != kWaiting);
+    switch (error) {
+      case kNoError:
+      case kWaiting:
+      case kYield:
+        return false;
+      default:
+        return true;
+    }
   }
 }
 
diff --git a/gpu/command_buffer/service/cmd_buffer_engine.h b/gpu/command_buffer/service/cmd_buffer_engine.h
index 964944d..59e99ab 100644
--- a/gpu/command_buffer/service/cmd_buffer_engine.h
+++ b/gpu/command_buffer/service/cmd_buffer_engine.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
diff --git a/gpu/command_buffer/service/common_decoder.cc b/gpu/command_buffer/service/common_decoder.cc
index a116d04..35eaf66 100644
--- a/gpu/command_buffer/service/common_decoder.cc
+++ b/gpu/command_buffer/service/common_decoder.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -330,4 +330,10 @@ error::Error CommonDecoder::HandleGetBucketData(
   return error::kNoError;
 }
 
+error::Error CommonDecoder::HandleYieldScheduler(
+    uint32 immediate_data_size,
+    const cmd::YieldScheduler& args) {
+  return error::kYield;
+}
+
 }  // namespace gpu
diff --git a/gpu/command_buffer/service/common_decoder_unittest.cc b/gpu/command_buffer/service/common_decoder_unittest.cc
index 8f88398..9b53a56 100644
--- a/gpu/command_buffer/service/common_decoder_unittest.cc
+++ b/gpu/command_buffer/service/common_decoder_unittest.cc
@@ -556,5 +556,11 @@ TEST_F(CommonDecoderTest, GetBucketData) {
   EXPECT_NE(error::kNoError, ExecuteCmd(cmd));
 }
 
+TEST_F(CommonDecoderTest, YieldScheduler) {
+  cmd::YieldScheduler cmd;
+  cmd.Init();
+  EXPECT_EQ(error::kYield, ExecuteCmd(cmd));
+}
+
 }  // namespace gpu
 
diff --git a/gpu/command_buffer/service/gpu_scheduler.cc b/gpu/command_buffer/service/gpu_scheduler.cc
index 1782dec..408d56d 100644
--- a/gpu/command_buffer/service/gpu_scheduler.cc
+++ b/gpu/command_buffer/service/gpu_scheduler.cc
@@ -146,16 +146,17 @@ void GpuScheduler::ProcessCommands() {
 
   error::Error error = error::kNoError;
   int commands_processed = 0;
-  while (commands_processed < commands_per_update_ && !parser_->IsEmpty()) {
+  while (commands_processed < commands_per_update_ &&
+         !parser_->IsEmpty()) {
     error = parser_->ProcessCommand();
-    if (error == error::kWaiting) {
-      break;
-    }
 
-    if (error::IsError(error)) {
+    if (error == error::kWaiting || error == error::kYield) {
+      break;
+    } else if (error::IsError(error)) {
       command_buffer_->SetParseError(error);
       return;
     }
+
     ++commands_processed;
     if (command_processed_callback_.get()) {
       command_processed_callback_->Run();