As my OctoPi installation was a bit slow on my RPi Zero I wanted to try overclocking it. I found a lot of different reports about overclockability and temperature, so I did some measurements myself.
Measuring RPi temperature and clock frequency
I used this script to run the CPU test from sysbench on all cores of the CPU in a loop and print the ARM frequency and temperature and also the throttle flags:
#!/bin/bash TIMEFORMAT=%Rs CORES=$(grep -c '^processor' /proc/cpuinfo 2>/dev/null) echo "Running sysbench --test=cpu --cpu-max-prime=2000 --num-threads=$CORES (CTRL-C quits)" for (( ; ; )) do # For Rasperry Pi systems echo "ARM $(vcgencmd measure_clock arm), $(vcgencmd measure_temp), $(vcgencmd get_throttled)" # For other systems #echo "$(lscpu | grep MHz), $(sensors | grep 'Core 0')" echo -n "Sysbench CPU "; time sysbench --test=cpu --cpu-max-prime=2000 --num-threads=$CORES run >/dev/null 2>&1 # echo -n "Sysbench Memory "; # time sysbench --test=memory --memory-block-size=1M --memory-total-size=10G --num-threads=$CORES run >/dev/null 2>&1 done
Running sysbench --test=cpu --cpu-max-prime=2000 --num-threads=1 (CTRL-C quits) ARM frequency(45)=700000000, temp=31.5'C, throttled=0x0 Sysbench CPU 22.118s ARM frequency(45)=1100000000, temp=39.0'C, throttled=0x0 Sysbench CPU 21.961s ...
Additionally I measured power consumption at 5V with a UNI-T UT61B meter. Note that the Pi model was a non-W RPi Zero (no heatsink, board upside down, so not much airflow, ~20°C room temperature) and had an active USB hub with a WiFi adapter (Ralink Technology, Corp. RT5370) attached. The current draw is for the whole system (RPi + hub + WiFi). I was connected the whole time through SSH. Here are some results:
speeds (arm / gpu / sdram) (MHz)
temperature (°C )
|Stock (1000 / 400 / 450)||291||380||44.5||24.2||No|
|1100 / 500 / 500||292||407||47.6||22.0||No|
|1150 / 550 / 550||293||418||49.2||21.0||No|
|1150 / 600 / 600||293||422||49.8||21.0||No|
|1200 / 550 / 550|
(did not boot)
So the takeaway is that you can overclock the Pi Zero by ~10-15%, it will not throttle and you actually have a decent performance gain. Cooling seems to be unnecessary. You have to try what works for your specific hardware though (ymmv). You could take this further by voiding your warranty and using “force_turbo” + “over_voltage” and trying higher frequencies. You can find all config.txt overclocking parameters here and the RetroPie wiki has an extensive entry about overclocking.
Here are the entries I used for /boot/config.txt:
# Modest overclock. See: https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md for parameters arm_freq=1100 over_voltage=4 core_freq=500 sdram_freq=500 over_voltage_sdram=2 # Maximum overclock. See: https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md for parameters arm_freq=1150 over_voltage=6 core_freq=600 sdram_freq=600 over_voltage_sdram=4