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

Revert of content: Use NumberOfProcessors() / 2 raster threads. (patchset #2 id:20001 of https://codereview.chromium.org/1143473002/)

Reason for revert:
Incorrect logic for determining if async uploads is used

Original issue's description:
> 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=
>
> Committed: https://crrev.com/4a0177a1dba8197f61021ff3b4f9426e45faaa62
> Cr-Commit-Position: refs/heads/master@{#330427}

TBR=danakj@chromium.org,enne@chromium.org,piman@chromium.org,vmpstr@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1136633006

Cr-Commit-Position: refs/heads/master@{#330520}

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* kThreadedRasterizationFeatureName = "threaded_rasterization";
 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 @@ bool IsImplSidePaintingEnabled() {
 }
 
 int NumberOfRendererRasterThreads() {
-  int num_raster_threads = base::SysInfo::NumberOfProcessors() / 2;
+  int num_raster_threads = 1;
 
-  // 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 =
+  // 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;
+  if (base::SysInfo::NumberOfProcessors() >= 4 && allow_extra_thread)
+    num_raster_threads = 2;
 
-  const base::CommandLine& command_line =
-      *base::CommandLine::ForCurrentProcess();
+  int force_num_raster_threads = ForceNumberOfRendererRasterThreads();
+  if (force_num_raster_threads)
+    num_raster_threads = force_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);
+  return num_raster_threads;
 }
 
 bool IsOneCopyUploadEnabled() {
@@ -260,6 +249,26 @@ 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();
@@ -374,9 +383,7 @@ base::DictionaryValue* GetFeatureStatus() {
           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 ||

content/browser/gpu/compositor_util.h

@@ -49,6 +49,10 @@ 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();