Sets android.ui to be in the fg stune group.

setThreadGroup(TOP_APP) will place a thread in the fg stune group but
not the top_app cpuset. This allows android.ui to get more runtime to
render transitions between activities without impacting its CPU
placement.

bug 29512132

Change-Id: I95e031975f83290f88ac6e538abf1062aea27ed4

core/java/android/os/Process.java

@@ -971,6 +971,9 @@ public class Process {
      * priority.
      * If the thread is a thread group leader, that is it's gettid() == getpid(),
      * then the other threads in the same thread group are _not_ affected.
+     *
+     * Does not set cpuset for some historical reason, just calls
+     * libcutils::set_sched_policy().
      */
     public static final native void setThreadGroup(int tid, int group)
             throws IllegalArgumentException, SecurityException;
@@ -992,6 +995,8 @@ public class Process {
      * priority threads alone.  group == THREAD_GROUP_BG_NONINTERACTIVE moves all
      * threads, regardless of priority, to the background scheduling group.
      * group == THREAD_GROUP_FOREGROUND is not allowed.
+     *
+     * Always sets cpusets.
      */
     public static final native void setProcessGroup(int pid, int group)
             throws IllegalArgumentException, SecurityException;

services/core/java/com/android/server/UiThread.java

@@ -17,6 +17,7 @@
 package com.android.server;
 
 import android.os.Handler;
+import android.os.Process;
 import android.os.Trace;
 
 /**
@@ -29,7 +30,9 @@ public final class UiThread extends ServiceThread {
     private static Handler sHandler;
 
     private UiThread() {
-        super("android.ui", android.os.Process.THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
+        super("android.ui", Process.THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
+        // Make sure UiThread is in the fg stune boost group
+        Process.setThreadGroup(Process.myTid(), Process.THREAD_GROUP_TOP_APP);
     }
 
     private static void ensureThreadLocked() {