Limit number of raster threads on Android.

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 2e46bdab05bce8b521f79150a1e0140e100400aa..635944fba1422c0de5b4a8f7b6fd4f702ab661f6 100644
--- a/content/browser/gpu/compositor_util.cc
+++ b/content/browser/gpu/compositor_util.cc
@@ -198,7 +198,15 @@ bool IsImplSidePaintingEnabled() {
 }
 
 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.