ARM with inactive CPUs

Sometimes, ARM systems default to having several of the CPUs turned off to save power. If this happens, you need to turn them back on before doing the ATLAS install, as seen here:

   http://elinux.org/Jetson/Performance

In case this page goes away, for my 4-core system I had to (as root):

   echo 0 > /sys/module/cpu_tegra/parameters/auto_hotplug
   echo 0 > /sys/devices/system/cpu/cpuquiet/tegra_cpuquiet/enable
   echo 1 > /sys/devices/system/cpu/cpu0/online
   echo 1 > /sys/devices/system/cpu/cpu1/online
   echo 1 > /sys/devices/system/cpu/cpu2/online
   echo 1 > /sys/devices/system/cpu/cpu3/online

On another system I had, the echo would not work, but copying cpu0's online file over all others did.