Allow specifying cores for cpu.sh script.

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
 }
 
+enable_cores() {
+  # $1: How many cores to enable.
+  for (( i=1; i<=$MAXID; i++ )); do
+    if [ "$i" -lt "$1" ]; then
+      echo 1 > $CPUPATH/cpu$i/online
+    else
+      echo 0 > $CPUPATH/cpu$i/online
+    fi
+  done
+}
+
 dual_core() {
   echo "Switching to dual-core mode"
-  for (( i=2; i<=$MAXID; i++ )); do
-    echo 0 > $CPUPATH/cpu$i/online
-  done
+  enable_cores 2
 }
 
 single_core() {
   echo "Switching to single-core mode"
-  for (( i=1; i<=$MAXID; i++ )); do
-    echo 0 > $CPUPATH/cpu$i/online
-  done
+  enable_cores 1
 }
 
 
 all_cores() {
   echo "Reactivating all CPU cores"
-  for (( i=1; i<=$MAXID; i++ )); do
-    echo 1 > $CPUPATH/cpu$i/online
-  done
+  enable_cores $((MAXID+1))
+}
+
+
+limit_cores() {
+  # $1: How many cores to enable.
+  echo "Limiting to $1 cores"
+  enable_cores $1
 }
 
 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
     ;;
+  limit_cores)
+    if [ $# -ne 2 ]; then
+      echo "Usage $0 limit_cores <num>"
+      exit 1
+    fi
+    limit_cores $2
+    ;;
   *)
-    echo "Usage: $0 fast|slow|default|singlecore|dualcore|all"
+    echo "Usage: $0 fast|slow|default|singlecore|dualcore|all|limit_cores"
     exit 1
     ;;
 esac