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Synchronous cluster switching interface for the ARM big.LITTLE switcher
-----------------------------------------------------------------------
The arm-bl-cpufreq driver provides a simple interface which models two
clusters as two performance points.
Within each CPU's cpufreq directory in sysfs
(/sys/devices/system/cpu/cpu?/cpufreq/):
cpuinfo_max_freq:
reports the dummy frequency value which corresponds to the "big"
cluster.
cpuinfo_min_freq:
reports the dummy frequency value which corresponds to the
"little" cluster.
cpuinfo_cur_freq:
reports the dummy frequency corresponding to the currently
running cluster.
To switch clusters, either the built-in "powersave" or "performance"
governors can be used to force the "little" or "big" cluster
respectively; or alternatively the "userspace" governor can be used,
The following script fragment demonstrates how the userspace governor
can be used to switch:
for x in /sys/devices/system/cpu/cpu[0-9]*; do
echo userspace >$x/cpufreq/scaling_governor
done
big_freq=`cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq`
little_freq=`cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq`
switch_to_big () {
echo $big_freq >/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
}
switch_to_little () {
echo $little_freq >/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
}
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