Revert of content: Use NumberOfProcessors() / 2 raster threads.

content/browser/gpu/compositor_util.cc

Index: content/browser/gpu/compositor_util.cc
diff --git a/content/browser/gpu/compositor_util.cc b/content/browser/gpu/compositor_util.cc
index 86227475a6f4cdb3129e3ce707379574e5a322da..a96cdeae4138e43adcfdccc3760e963dc2cce6a9 100644
--- a/content/browser/gpu/compositor_util.cc
+++ b/content/browser/gpu/compositor_util.cc
@@ -10,7 +10,6 @@
 #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"
@@ -33,7 +32,7 @@
 const char* kMultipleRasterThreadsFeatureName = "multiple_raster_threads";
 
 const int kMinRasterThreads = 1;
-const int kMaxRasterThreads = 16;
+const int kMaxRasterThreads = 64;
 
 const int kMinMSAASampleCount = 0;
 
@@ -211,30 +210,20 @@
 }
 
 int NumberOfRendererRasterThreads() {
-  int num_raster_threads = base::SysInfo::NumberOfProcessors() / 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 =
+  int num_raster_threads = 1;
+
+  // 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 (async_uploads_is_used)
-    --num_raster_threads;
-
-  const base::CommandLine& command_line =
-      *base::CommandLine::ForCurrentProcess();
-
-  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);
+  if (base::SysInfo::NumberOfProcessors() >= 4 && allow_extra_thread)
+    num_raster_threads = 2;
+
+  int force_num_raster_threads = ForceNumberOfRendererRasterThreads();
+  if (force_num_raster_threads)
+    num_raster_threads = force_num_raster_threads;
+
+  return num_raster_threads;
 }
 
 bool IsOneCopyUploadEnabled() {
@@ -258,6 +247,26 @@
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
   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() {
@@ -374,9 +383,7 @@
           status += "_force";
       }
       if (gpu_feature_info.name == kMultipleRasterThreadsFeatureName) {
-        const base::CommandLine& command_line =
-            *base::CommandLine::ForCurrentProcess();
-        if (command_line.HasSwitch(switches::kNumRasterThreads))
+        if (ForceNumberOfRendererRasterThreads() > 0)
           status += "_force";
       }
       if (gpu_feature_info.name == kThreadedRasterizationFeatureName ||