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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="iocost.conf" xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>iocost.conf</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>iocost.conf</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>iocost.conf</refname>
    <refpurpose>Configuration files for the iocost solution manager</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para>
      <filename>/etc/systemd/iocost.conf</filename>
      <filename>/etc/systemd/iocost.conf.d/*.conf</filename>
    </para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>This file configures the behavior of <literal>iocost</literal>, a tool mostly used by
    <citerefentry><refentrytitle>systemd-udevd</refentrytitle><manvolnum>8</manvolnum></citerefentry> rules
    to automatically apply I/O cost solutions to <filename>/sys/fs/cgroup/io.cost.*</filename>.</para>

    <para>The qos and model values are calculated based on benchmarks collected on the
    <ulink url="https://github.com/iocost-benchmark/iocost-benchmarks">iocost-benchmark</ulink>
    project and turned into a set of solutions that go from most to least isolated.
    Isolation allows the system to remain responsive in face of high I/O load.
    Which solutions are available for a device can be queried from the udev metadata attached to it. By
    default the naive solution is used, which provides the most bandwidth.</para>
  </refsect1>

  <xi:include href="standard-conf.xml" xpointer="main-conf" />

  <refsect1>
    <title>Options</title>

    <para>All options are configured in the [IOCost] section:</para>

    <variablelist class='config-directives'>

      <varlistentry>
        <term><varname>TargetSolution=</varname></term>

        <listitem><para>Chooses which I/O cost solution (identified by named string) should be used
        for the devices in this system. The known solutions can be queried from the udev metadata
        attached to the devices. If a device does not have the specified solution, the first one
        listed in <varname>IOCOST_SOLUTIONS</varname> is used instead.</para>

        <para>E.g. <literal>TargetSolution=isolated-bandwidth</literal>.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
      <member><ulink url="https://github.com/iocost-benchmark/iocost-benchmarks">The
      iocost-benchmarks github project</ulink></member>
      <member><ulink url="https://github.com/facebookexperimental/resctl-demo/tree/main/resctl-bench/doc">The resctl-bench
      documentation details how the values are obtained</ulink></member>
    </simplelist></para>
  </refsect1>

</refentry>
