Seastar Perftune

ScyllaDB's Seastar Perftune helps you run ScyllaDB with its maximum performance. The perftune.py <https://github.com/scylladb/seastar/blob/master/scripts/perftune.py>_ script handles network and disk tuning, reassigning IRQs to specific CPU cores and freeing the other cores for ScyllaDB’s exclusive use.

More specifically, running the script will:

• Ban relevant IRQs from being moved by irqbalance.
• Configure various system parameters in /proc/sys.
• Distribute the IRQs (using SMP affinity configuration) among CPUs according to the irq_cpu_mask value. Note that more than one physical core will be used for IRQ handling for large machines.

To ensure that the tuning persists after a host reboot, we recommend creating a systemd unit that will run on host startup and re-tune the hosts.

perftune.yaml

The perfrune.yaml file is the output file of the perftune.py script (with the --dump-options-file option enabled). The script determines the irq_cpu_mask and prints it to perftume.yaml on the first machine.

It's important to use the same irq_cpu_mask value on other machines, even if more machines are added to the cluster, to avoid a mixed-cluster situation.

Note that perftune.yaml is generated only if the file doesn’t exist.

Available Options

You can run perftune.py with the following options:

.. list-table:: :widths: 30 70 :header-rows: 1

• • Option
  • Description
• • --arfs
  • Enables/disables aRFS.
• • --cpu-mask
  • The masks of cores to use. The default is all available cores.
• • --dev
  • Specifies the device to optimize; for example, sda1. You can use it more than once to specify multiple devices.
• • --dir
  • Specifies the directory to optimize. You can use it more than once to specify multiple directories.
• • --dry-run
  • Prints recommendations on what to do without taking any action.
• • --dump-options-file
  • Prints the configuration YAML file containing the current configuration.
• • --get-cpu-mask
  • Prints the CPU mask to be used for computation.
• • --get-cpu-mask-quiet
  • Prints the CPU mask to be used for computation. Prints the zero CPU set if that's what it is.
• • --get-irq-cpu-mask
  • Prints the CPU mask to be used for IRQs binding.
• • --irq-core-auto-detection-ratio
  • Specifies a ratio for IRQ mask auto-detection. For example, if 8 is given and auto-detection is requested, a single IRQ CPU core is going to be allocated for every 8 CPU cores out of available according to the cpu_mask value. The default is 16.
• • --irq-cpu-mask
  • The mask of the cores to be used for IRQs binding.
• • --nic
  • The network interface name. The default is eth0. You can use it more than once to specify multiple interfaces.
• • --num-rx-queues
  • Sets a given number of Rx queues.
• • --options-file
  • The configuration YAML file.

• • --tune

  • Specifies the components to configure. You can use it more than once to specify multiple values. The available values are:

    • net - Enables tuning the network.
    • disks - Enables tuning the disks.
    • system - Enables tuning system-related components.
• • --tune-clock
  • Forces tuning of /system/clocksource. The default is false. Requires the --tune option.
• • --verbose
  • Provides additional details about operations and their results.
• • --write-back-cache
  • Enables/disables the write back write cache mode.