Limit number of raster threads on Android.

content/browser/gpu/compositor_util.cc

 // Copyright (c) 2012 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.
 
 #include "content/browser/gpu/compositor_util.h"
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 180 matching lines @@
 
 bool IsImplSidePaintingEnabled() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
   if (command_line.HasSwitch(switches::kDisableImplSidePainting))
     return false;
   return true;
 }
 
 int NumberOfRendererRasterThreads() {
-  int num_raster_threads = base::SysInfo::NumberOfProcessors() / 2;
+  int num_processors = base::SysInfo::NumberOfProcessors();
+
+#if defined(OS_ANDROID)
+  // Android may report 6 to 8 CPUs for big.LITTLE configurations.
+  // Limit the number of raster threads based on maximum of 4 big cores.
+  num_processors = std::min(num_processors, 4);
+#endif
+
+  int num_raster_threads = num_processors / 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

[no sievers, 2015/06/09 18:26:30]

So what about this stuff?
It sounds like it's talking about the transfer thread which is actually only
enabled on certain devices (see async_pixel_transfer_manager_android.cc). Plus
it will be going away entirely.

Q: Do we want to be subtracting a thread here if we are using 'idle uploads'?

[reveman, 2015/06/09 19:28:13]

Not needed in that case but it's hard to know that from here. With async uploads
hopefully going away soon I don't think it's worth much time trying to improve
this.

   // uploads is in use.
   bool async_uploads_is_used =
       !IsZeroCopyUploadEnabled() && !IsOneCopyUploadEnabled();
   if (async_uploads_is_used)
     --num_raster_threads;
 
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
 
   if (command_line.HasSwitch(switches::kNumRasterThreads)) {
@@ skipping 214 matching lines @@
     }
   }
   return problem_list;
 }
 
 std::vector<std::string> GetDriverBugWorkarounds() {
   return GpuDataManagerImpl::GetInstance()->GetDriverBugWorkarounds();
 }
 
 }  // namespace content