Power Saving

Wake-on-LAN

When the cluster is setup it is often not needed to have the machines powered when there is no job in the queue.

What you can setup is a simple Wake-on-LAN script that will only wakeup the machines when there is job in the queue waiting.

For examplary purposes we document a script here that works on a low power Raspberry PI that we have active in our local network, but any simple microcontroller that has HTTP capabilites will.

#!/bin/bash
# filename: wake_machine.sh


# Install this script as a cronjob
# m h  dom mon dow   command
# 15\/* * * * * bash /home/pi/wake_machine.sh

## You need the wakeonlan and the jq package installed
## sudo apt install wakeonlan jq -y


output=$(curl "https://api.green-coding.io/v1/jobs?machine_id=7&state=WAITING" --silent  |  jq '.["data"] | length')

# Check if the output is a specific string
if [[ "$output" =~ ^[0-9]+$ && $output -ne 0 ]]; then
    echo "Having waiting jobs. Sending Wake on LAN magic packet ..."

    # Please replace '80:1B:3E:A8:26:19' with your machines MAC address
    # Using port 1234 will usually work. If you run into issues try port 9, 8 or 7 also
    # Do not use the IP address of the machine, but the broadcast address (usually the last number block must be replaced by 255)
    wakeonlan -i 10.1.0.255 -p 1234 80:1B:3E:A8:26:19

    echo "Wake on LAN magic packet send!"
else
    echo "Command output is '0'. No other program started."
fi

Turning machine off on empty queue

To use this functionality you should have Wake-on-LAN activated.

You can then set the shutdown_on_job_no to either “poweroff” or “suspend” and the machine will turn off when the job queue is empty.

cluster:
  client:
    ...  
    shutdown_on_job_no: suspend

In order for the shutdown to be triggered by the client.py you must allow the sudo call without password in an /etc/sudoers.d/ entry. Please choose the line that is appropriate for you depending on if you want to suspend or poweroff.

Example:

echo 'ALL ALL=(ALL) NOPASSWD:/usr/bin/systemctl suspend' | sudo tee /etc/sudoers.d/green-coding-shutdown # for systems that support suspend
echo 'ALL ALL=(ALL) NOPASSWD:/usr/bin/systemctl poweroff' | sudo tee -a /etc/sudoers.d/green-coding-shutdown # for systems that only can shutdown
sudo chmod 500 /etc/sudoers.d/green-coding-shutdown

Activating Wake-On-Lan

In rare circumstances Wake-On-Lan is not active on the machine.

Check the following:

  • Check the BIOS if Wake-On-Lan is enabled.
    • If no option is present it might not be configurable through the BIOS
  • Check $ sudo ethtool <YOUR_INTERFACE>
    • Output should list: Wake-on: g

If the value is d it is disabled. You can activate it temporarily until the next suspend / reboot with: $ sudo ethtool -s <YOUR_INTERFACE> wol g

Persist it with a systemd service: $ sudo nano /etc/systemd/system/wol.service

[Unit]
Description=Enable Wake-on-LAN on YOUR_INTERFACE
After=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
ExecStart=/sbin/ethtool -s <YOUR_INTERFACE> wol g
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Activating suspend to ram

Instead of powering the system off you can also bring it to a suspend mode.

To really save power your system should support Suspend to RAM.

Check $ cat /sys/power/state. It should list mem as part of the output.

This means the OS supports bringing the system to Suspend to RAM.

Now check $ cat /sys/power/mem_sleep. A sample output looks like this:

s2idle [deep]

If deep is in brackets all is good. If s2idle is in brackets you have the wrong setting. To change the setting you can set a kernel boot parameter:

Add mem_sleep_default=deep to GRUB: GRUB_CMDLINE_LINUX_DEFAULT="... mem_sleep_default=deep" Then $ sudo update-grub and reboot.

If your output is only [s2idle] then your network card driver or some other component does not support Suspend to Ram or is prohibiting it’s activation. For instance disabling CPU power saving modes can block this setting.

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