Check in "cpu.sh" script to control CPU governor/cores on Linux

This can help with reproducing stability bugs or performance issues.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/485763003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23222 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/cpu.sh

+#!/bin/bash
+# Copyright 2014 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+CPUPATH=/sys/devices/system/cpu
+
+MAXID=$(cat $CPUPATH/present | awk -F- '{print $NF}')
+
+set_governor() {
+  echo "Setting CPU frequency governor to \"$1\""
+  for (( i=0; i<=$MAXID; i++ )); do
+    echo "$1" > $CPUPATH/cpu$i/cpufreq/scaling_governor
+  done
+}
+
+dual_core() {
+  echo "Switching to dual-core mode"
+  for (( i=2; i<=$MAXID; i++ )); do
+    echo 0 > $CPUPATH/cpu$i/online
+  done
+}
+
+single_core() {
+  echo "Switching to single-core mode"
+  for (( i=1; i<=$MAXID; i++ )); do
+    echo 0 > $CPUPATH/cpu$i/online
+  done
+}
+
+
+all_cores() {
+  echo "Reactivating all CPU cores"
+  for (( i=2; i<=$MAXID; i++ )); do
+    echo 1 > $CPUPATH/cpu$i/online
+  done
+}
+
+case "$1" in
+  fast | performance)
+    set_governor "performance"
+    ;;
+  slow | powersave)
+    set_governor "powersave"
+    ;;
+  default | ondemand)
+    set_governor "ondemand"
+    ;;
+  dualcore | dual)
+    dual_core
+    ;;
+  singlecore | single)
+    single_core
+    ;;
+  allcores | all)
+    all_cores
+    ;;
+  *)
+    echo "Usage: $0 fast|slow|default|singlecore|dualcore|all"
+    exit 1
+    ;;
+esac