Revert 235428 "Revert 234915 "Revert 234758 "gpu: Remove redunda..."

> Revert 234915 "Revert 234758 "gpu: Remove redundant calls from C..."
> 
> > Revert 234758 "gpu: Remove redundant calls from CommandBufferHel..."
> > 
> > > gpu: Remove redundant calls from CommandBufferHelper::GetSpace() and optimize it.
> > > 
> > > GetSpace() was calling AllocateRingBuffer() followed by WaitForAvailableEntries(). However, WaitForAvailable() was also calling AllocateRingBuffer() which ended up being redundant. We remove the redundant AllocateRingBuffer() call from GetSpace() in this patch.
> > > 
> > > Also, we add a "fast-path" to return memory as soon as possible without issuing any GL commands if a suitably allocated buffer is already present and can satisfy the request immediately. 
> > > 
> > > BUG=181711
> > > 
> > > Review URL: https://codereview.chromium.org/63513002
> > 
> > TBR=kaanb@chromium.org
> > 
> > Review URL: https://codereview.chromium.org/64833010
> 
> TBR=kaanb@chromium.org
> 
> Review URL: https://codereview.chromium.org/74123003

TBR=kaanb@chromium.org

Review URL: https://codereview.chromium.org/59153014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236069 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 46 insertions, 57 deletions

diff --git a/gpu/command_buffer/client/cmd_buffer_helper.cc b/gpu/command_buffer/client/cmd_buffer_helper.cc
index 3b9599e..11219ed 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper.cc
@@ -12,6 +12,12 @@
 
 namespace gpu {
 
+const int kCommandsPerFlushCheck = 100;
+
+#if !defined(OS_ANDROID)
+const double kFlushDelay = 1.0 / (5.0 * 60.0);
+#endif
+
 CommandBufferHelper::CommandBufferHelper(CommandBuffer* command_buffer)
     : command_buffer_(command_buffer),
       ring_buffer_id_(-1),
@@ -190,7 +196,12 @@ void CommandBufferHelper::WaitForToken(int32 token) {
 // around, adding a noops. Thus this function may change the value of put_. The
 // function will return early if an error occurs, in which case the available
 // space may not be available.
-bool CommandBufferHelper::WaitForAvailableEntries(int32 count) {
+void CommandBufferHelper::WaitForAvailableEntries(int32 count) {
+  AllocateRingBuffer();
+  if (!usable()) {
+    return;
+  }
+  DCHECK(HaveRingBuffer());
   DCHECK(count < total_entry_count_);
   if (put_ + count > total_entry_count_) {
     // There's not enough room between the current put and the end of the
@@ -204,7 +215,7 @@ bool CommandBufferHelper::WaitForAvailableEntries(int32 count) {
         // Do not loop forever if the flush fails, meaning the command buffer
         // reader has shutdown.
         if (!FlushSync())
-          return false;
+          return;
       }
     }
     // Insert Noops to fill out the buffer.
@@ -223,29 +234,46 @@ bool CommandBufferHelper::WaitForAvailableEntries(int32 count) {
       // Do not loop forever if the flush fails, meaning the command buffer
       // reader has shutdown.
       if (!FlushSync())
-        return false;
+        return;
     }
   }
-  FlushIfNeeded();
-  return true;
+  // Force a flush if the buffer is getting half full, or even earlier if the
+  // reader is known to be idle.
+  int32 pending =
+      (put_ + total_entry_count_ - last_put_sent_) % total_entry_count_;
+  int32 limit = total_entry_count_ /
+      ((get_offset() == last_put_sent_) ? 16 : 2);
+  if (pending > limit) {
+    Flush();
+  } else if (flush_automatically_ &&
+             (commands_issued_ % kCommandsPerFlushCheck == 0)) {
+#if !defined(OS_ANDROID)
+    // Allow this command buffer to be pre-empted by another if a "reasonable"
+    // amount of work has been done. On highend machines, this reduces the
+    // latency of GPU commands. However, on Android, this can cause the
+    // kernel to thrash between generating GPU commands and executing them.
+    clock_t current_time = clock();
+    if (current_time - last_flush_time_ > kFlushDelay * CLOCKS_PER_SEC)
+      Flush();
+#endif
+  }
 }
 
 CommandBufferEntry* CommandBufferHelper::GetSpace(uint32 entries) {
-  ++commands_issued_;
-  if (HaveRingBuffer() && usable() && entries <= SpaceAvailableImmediately()) {
-    FlushIfNeeded();
-    return GetSpaceForEntries(entries);
-  }
-
   AllocateRingBuffer();
   if (!usable()) {
     return NULL;
   }
   DCHECK(HaveRingBuffer());
-  if (!WaitForAvailableEntries(entries))
-    return NULL;
-
-  return GetSpaceForEntries(entries);
+  ++commands_issued_;
+  WaitForAvailableEntries(entries);
+  CommandBufferEntry* space = &entries_[put_];
+  put_ += entries;
+  DCHECK_LE(put_, total_entry_count_);
+  if (put_ == total_entry_count_) {
+    put_ = 0;
+  }
+  return space;
 }
 
 }  // namespace gpu
diff --git a/gpu/command_buffer/client/cmd_buffer_helper.h b/gpu/command_buffer/client/cmd_buffer_helper.h
index 4d334e9..a50dc7b 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper.h
+++ b/gpu/command_buffer/client/cmd_buffer_helper.h
@@ -72,9 +72,7 @@ class GPU_EXPORT CommandBufferHelper {
   // Parameters:
   //   count: number of entries needed. This value must be at most
   //     the size of the buffer minus one.
-  // Returns:
-  //   true on success, false on failure.
-  bool WaitForAvailableEntries(int32 count);
+  void WaitForAvailableEntries(int32 count);
 
   // Inserts a new token into the command buffer. This token either has a value
   // different from previously inserted tokens, or ensures that previously
@@ -245,43 +243,6 @@ class GPU_EXPORT CommandBufferHelper {
 
   bool AllocateRingBuffer();
   void FreeResources();
-  CommandBufferEntry* GetSpaceForEntries(uint32 entries) {
-    CommandBufferEntry* space = &entries_[put_];
-    put_ += entries;
-    DCHECK_LE(put_, total_entry_count_);
-    if (put_ == total_entry_count_) {
-      put_ = 0;
-    }
-    return space;
-  }
-
-  uint32 SpaceAvailableImmediately() {
-    return get_offset() > put_ ? get_offset() - put_
-      : total_entry_count_ - put_;
-  }
-
-  void FlushIfNeeded() {
-    const int kCommandsPerFlushCheck = 100;
-    const double kFlushDelay = 1.0 / (5.0 * 60.0);
-
-    // Force a flush if the buffer is getting half full, or even earlier if the
-    // reader is known to be idle.
-    int32 pending =
-      (put_ + total_entry_count_ - last_put_sent_) % total_entry_count_;
-    int32 limit = total_entry_count_ /
-      ((get_offset() == last_put_sent_) ? 16 : 2);
-    if (pending > limit) {
-      Flush();
-    } else if (flush_automatically_ &&
-               (commands_issued_ % kCommandsPerFlushCheck == 0)) {
-      // Allow this command buffer to be pre-empted by another if a "reasonable"
-      // amount of work has been done. On highend machines, this reduces the
-      // latency of GPU commands.
-      clock_t current_time = clock();
-      if (current_time - last_flush_time_ > kFlushDelay * CLOCKS_PER_SEC)
-        Flush();
-    }
-  }
 
   CommandBuffer* command_buffer_;
   int32 ring_buffer_id_;
diff --git a/gpu/command_buffer/client/cmd_buffer_helper_test.cc b/gpu/command_buffer/client/cmd_buffer_helper_test.cc
index d92a033..bd0e86e 100644
--- a/gpu/command_buffer/client/cmd_buffer_helper_test.cc
+++ b/gpu/command_buffer/client/cmd_buffer_helper_test.cc
@@ -240,7 +240,7 @@ TEST_F(CommandBufferHelperTest, TestAvailableEntries) {
   AddCommandWithExpect(error::kNoError, kUnusedCommandId + 4, 2, args);
 
   // Ask for 5 entries.
-  EXPECT_TRUE(helper_->WaitForAvailableEntries(5));
+  helper_->WaitForAvailableEntries(5);
 
   CommandBufferOffset put = get_helper_put();
   CheckFreeSpace(put, 5);
@@ -248,7 +248,7 @@ TEST_F(CommandBufferHelperTest, TestAvailableEntries) {
   // Add more commands.
   AddCommandWithExpect(error::kNoError, kUnusedCommandId + 5, 2, args);
 
-  // Wait until everything is done.
+  // Wait until everything is done done.
   helper_->Finish();
 
   // Check that the commands did happen.