Re-land: content: Use NumberOfProcessors() / 2 raster threads.

4 raster threads improve performance on 8 core machines.
8 core machines might not be a priority but it seems
like an unnecessary limitation to have.

BUG=

Review URL: https://codereview.chromium.org/1143473002

Cr-Commit-Position: refs/heads/master@{#330555}

content/browser/gpu/compositor_util.cc

@@ -10,6 +10,7 @@
 #include "base/strings/string_number_conversions.h"
 #include "base/sys_info.h"
 #include "build/build_config.h"
+#include "cc/base/math_util.h"
 #include "cc/base/switches.h"
 #include "content/browser/gpu/gpu_data_manager_impl.h"
 #include "content/public/common/content_switches.h"
@@ -32,7 +33,7 @@ const char* kThreadedRasterizationFeatureName = "threaded_rasterization";
 const char* kMultipleRasterThreadsFeatureName = "multiple_raster_threads";
 
 const int kMinRasterThreads = 1;
-const int kMaxRasterThreads = 64;
+const int kMaxRasterThreads = 16;
 
 const int kMinMSAASampleCount = 0;
 
@@ -210,20 +211,30 @@ bool IsImplSidePaintingEnabled() {
 }
 
 int NumberOfRendererRasterThreads() {
-  int num_raster_threads = 1;
+  int num_raster_threads = base::SysInfo::NumberOfProcessors() / 2;
 
-  // Async uploads uses its own thread, so allow an extra thread when async
-  // uploads is not in use.
-  bool allow_extra_thread =
-      IsZeroCopyUploadEnabled() || IsOneCopyUploadEnabled();
-  if (base::SysInfo::NumberOfProcessors() >= 4 && allow_extra_thread)
-    num_raster_threads = 2;
+  // Async uploads is used when neither zero-copy nor one-copy is enabled and
+  // it uses its own thread, so reduce the number of raster threads when async
+  // uploads is in use.
+  bool async_uploads_is_used =
+      !IsZeroCopyUploadEnabled() && !IsOneCopyUploadEnabled();
+  if (async_uploads_is_used)
+    --num_raster_threads;
 
-  int force_num_raster_threads = ForceNumberOfRendererRasterThreads();
-  if (force_num_raster_threads)
-    num_raster_threads = force_num_raster_threads;
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
 
-  return num_raster_threads;
+  if (command_line.HasSwitch(switches::kNumRasterThreads)) {
+    std::string string_value = command_line.GetSwitchValueASCII(
+        switches::kNumRasterThreads);
+    if (!base::StringToInt(string_value, &num_raster_threads)) {
+      DLOG(WARNING) << "Failed to parse switch " <<
+          switches::kNumRasterThreads  << ": " << string_value;
+    }
+  }
+
+  return cc::MathUtil::ClampToRange(num_raster_threads, kMinRasterThreads,
+                                    kMaxRasterThreads);
 }
 
 bool IsOneCopyUploadEnabled() {
@@ -249,26 +260,6 @@ bool IsZeroCopyUploadEnabled() {
   return command_line.HasSwitch(switches::kEnableZeroCopy);
 }
 
-int ForceNumberOfRendererRasterThreads() {
-  const base::CommandLine& command_line =
-      *base::CommandLine::ForCurrentProcess();
-
-  if (!command_line.HasSwitch(switches::kNumRasterThreads))
-    return 0;
-  std::string string_value =
-      command_line.GetSwitchValueASCII(switches::kNumRasterThreads);
-  int force_num_raster_threads = 0;
-  if (base::StringToInt(string_value, &force_num_raster_threads) &&
-      force_num_raster_threads >= kMinRasterThreads &&
-      force_num_raster_threads <= kMaxRasterThreads) {
-    return force_num_raster_threads;
-  } else {
-    DLOG(WARNING) << "Failed to parse switch " <<
-        switches::kNumRasterThreads  << ": " << string_value;
-    return 0;
-  }
-}
-
 bool IsGpuRasterizationEnabled() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
@@ -383,7 +374,9 @@ base::DictionaryValue* GetFeatureStatus() {
           status += "_force";
       }
       if (gpu_feature_info.name == kMultipleRasterThreadsFeatureName) {
-        if (ForceNumberOfRendererRasterThreads() > 0)
+        const base::CommandLine& command_line =
+            *base::CommandLine::ForCurrentProcess();
+        if (command_line.HasSwitch(switches::kNumRasterThreads))
           status += "_force";
       }
       if (gpu_feature_info.name == kThreadedRasterizationFeatureName ||

content/browser/gpu/compositor_util.h

@@ -49,10 +49,6 @@ CONTENT_EXPORT bool IsForceGpuRasterizationEnabled();
 // Returns the number of raster threads to use for compositing.
 CONTENT_EXPORT int NumberOfRendererRasterThreads();
 
-// Returns the number of raster threads to use for compositing that are forced
-// by the command line.
-CONTENT_EXPORT int ForceNumberOfRendererRasterThreads();
-
 // Returns true if using cc Surfaces is allowed.
 CONTENT_EXPORT bool UseSurfacesEnabled();