# Setup BananaPI for benchmarking

The goal of this documentation is to get a linux image running on a
bananaPI board that allows for very isolated benchmarks showing full
time distributions of the measurement runs.

## Base Setup

First step is to get a linux image running on the banana PI. Armbian worked very well for us,
follow these setups to get it up and running:

- Download the mainline base kernel from armbian: https://www.armbian.com/bananapi-m3/#kernels-archive-all
- Unbpack the download
- Prepare a micro SD card for flashing
- Use etcher (https://www.balena.io/etcher/) or similar to burn the image on the sd card
- Insert the micro SD card into the banana PI and power it on
- Follow the instructions to setup an user account (best done using HDMI out and keyboard attatched)
- Test network connection/ssh login (armbian from our experience just works, that why we chose it)

## Tweaking Scheduler, CPU and Interrupts

We would like to get very little dispersion through system jitter. We recommend tweaking the
scheduler, CPU and interrupt settings before running benchmarks.

See the sub-sections below for the individual measures. ***Before running tests make sure to
run the following scripts:***
- `sudo ./setup_cpu.sh`
- `sudo ./map_interrupts_core_0.sh`
- `sudo ./setup_rt.sh`

Then start your tests manually mapped to cores 1 to 7.

### Pin all other processes to core 0

To further reduce inference with our controlled benchmark environment we map all non related
processes to core 0 of the system, running our benchmarks on cores 1 to 7.

The system uses system.d, which makes this the simplest point to change the default process affinity.
Edit the file `/etc/systemd/system.conf` and set `CPUAffinity=0`. This will make all processes forked
from system.d run on core 0. Benchmarks can then be manually mapped to different cores.

***BEFORE TESTS***: to make the config apply ***restart your system***

### CPU frequency

Limiting the frequency to 1GHz makes sure that the banana PI dose not throttle during the tests.
Additionally, disabling any dynamic frequency scaling makes tests more reproducable.

Create a file called 'setup_cpu.sh' and modify it with 'chmod +x setup_cpu.sh':
```shell script
echo "Writing frequency utils settings file..."
echo "ENABLE=true
MIN_SPEED=1008000
MAX_SPEED=1008000
GOVERNOR=performance" > vim /etc/default/cpufrequtils

echo "Restarting frequency utils service..."

echo "Done!"
echo "Try ./watch_cpu.sh to see  if everything worked."
echo "Test your cooling by stressing the cpu and watching the temperature output."
```

Create a file called 'watch_cpu.sh' and modify it with 'chmod +x watch_cpu.sh':
````shell script
echo "Max Frequencies"
cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_max_freq

echo "Actual Frequencies"
cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq

echo "Temps.."
cat /sys/class/thermal/thermal_zone*/temp
````

***BEFORE TESTS***:
To setup the CPU run ***`sudo ./setup_cpu.sh`*** before your tests. To see that the change worked
and the temperatures hold stable use the `./watch_cpu.sh` script.

### Map interrupts to core 0

Interrupts can infer with our benchmarks. We therefore map them to core 0 if possible and run our tests on
cores 1 to 7.

Create a file called 'map_interrupts_core_0.sh' and modify it with 'chmod +x map_interrupts_core_0.sh':
```shell script
#!/bin/bash

echo "Try to map interrupts to core 0."
echo "Some might fail because they can not be  mapped (e.g. core specific timers)."
echo ""
echo ""

for dir in /proc/irq/*/
do
	echo "Mapping $dir ..."
	echo 1 > $dir/smp_affinity
done
```

***BEFORE TESTS***: map the interrupts to core 0 using ***`sudo ./map_interrupts_core_0.sh`***

### Full time slices to RT scheduler

The RT scheduler in linux by default leaves some fraction of its scheduling time to non RT processes,
leaving the system in a responsive state if a RT application eats all CPU. We do not want this, as we
try to get a very predictable behavior in our RT scheduler.

Create a file called 'setup_rt.sh' and modify it with 'chmod +x setup_rt.sh':
```shell script
sysctl -w kernel.sched_rt_runtime_us=-1
sysctl -w kernel.sched_rt_period_us=1000000
````

***BEFORE TESTS***: give full time slices to RT tasks ***`sudo ./setup_rt.sh`***

## Running Tests

***Before running tests make sure to run the following scripts:***
- `sudo ./setup_cpu.sh`
- `sudo ./map_interrupts_core_0.sh`
- `sudo ./setup_rt.sh`

To run the tests use the following (or a similar command with different rt policy):

`taskset FFFE chrt -rr 80 sudo -u $SUDO_USER <benchmark>`

This maps the process to all cores but core 0 and runs them using the round robin real time schedule.
Rplace -rr with --fifo to use the first in first out scheduler.