It is said to overclock Raspberry Pi one has to upgrade the system:
sudo apt-get update && sudo apt-get install raspberrypi* raspi-config
Then configure it with raspi-config utility:
sudo raspi-config
It is good anyhow to check the system version first:
uname -a
Linux raspberrystar.pinkaccordions.org 3.2.27+ #174 PREEMPT Wed Sep 26 14:09:47 BST 2012 armv6l GNU/Linux
The kernel is up to date. Inspecting raspi-config I have discovered it is not updated, but I prefer to configure the system via CLI (command line or console) interface rather than GUI one (no need to connect the RPi to a TV set which is in another room:-). So I decided not to upgrade the system but rather manually configure it. To achieve overclocking one has to add the following lines to /boot/config.txt file:
pi@raspberrystar ~ $ sudo vim /boot/config.txt
## add the following:
temp_limit=80
arm_freq=900
sdram_freq=500
Now reboot:
pi@raspberrystar ~ $ sudo reboot
Check the dmesg:
pi@raspberrystar ~ $ dmesg | grep 7000
[ 1.956412] bcm2835-cpufreq: min=700000 max=900000 cur=700000
CPU frequency is still 700Mhz. To increase it one has to edit scaling_governor file:
pi@raspberrystar ~ $ sudo bash
root@raspberrystar:/home/pi#
echo "performance" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
## check if the above works:-)
pi@raspberrystar ~ $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
performance
# display available options:
pi@raspberrystar ~ $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
conservative ondemand userspace powersave performance
The ondemand option allows for adjusting CPU frequency depending on CPU utilization.
Without any further reboot the new settings work:
# check current CPU frequency
pi@raspberrystar ~ $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
900000
There is even a temperature sensor available so one can check if the CPU is not overheated:
# check processor temperature:
pi@raspberrystar ~ $ /opt/vc/bin/vcgencmd measure_temp
temp=46.5'C
To boot the system with scaling_governor set to appropriate value one has to edit /etc/rc.local:
pi@raspberrystar ~ $ sudo vim /etc/rc.local
# Add the following line
# echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
I have performed a simple test:
#!/bin/bash
#
N=5
START=$(date +%s)
for ((i=1;i<=$N;i++ )) ; do
echo "**** Iteration $i ****"
STARTI=$(date +%s)
perl -e 'for ($i=0;$i<=10000000;$i++) { $s .= "xx"; }'
ENDI=$(date +%s) ; TOTALI=$(( $ENDI - $STARTI ))
echo "*** $TOTALI s."
done
END=$(date +%s)
TOTAL=$(( $END - $START ))
MEAN=`awk -v m=$TOTAL -v n=$N 'BEGIN { print m/n }'`
echo "total: " $TOTAL "mean: " $MEAN
##
The test uses the following perl program:
perl -e 'for ($i=0;$i<=10000000;$i++) { $s .= "xx"; }'
Because computing time can vary, the program has to be run N times and the mean time is reported.
My Rpi runs 28--29s at 700 Mhz, 25,8s at 800 Mhz and 21s at 900 Mhz.
So running at 900 Mhz results in almost 30% reduction of computing time.
