IOCOST.CONF(5) iocost.conf IOCOST.CONF(5)
NAME
iocost.conf - Configuration files for the iocost solution manager
SYNOPSIS
/etc/systemd/iocost.conf /etc/systemd/iocost.conf.d/*.conf
DESCRIPTION
This file configures the behavior of "iocost", a tool mostly used by
systemd-udevd(8) rules to automatically apply I/O cost solutions to
/sys/fs/cgroup/io.cost.*.
The qos and model values are calculated based on benchmarks collected on
the iocost-benchmark[1] 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.
CONFIGURATION DIRECTORIES AND PRECEDENCE
The default configuration is set during compilation, so configuration is
only needed when it is necessary to deviate from those defaults. The
main configuration file is loaded from one of the listed directories in
order of priority, only the first file found is used: /etc/systemd/,
/run/systemd/, /usr/local/lib/systemd/ [2], /usr/lib/systemd/. The
vendor version of the file contains commented out entries showing the
defaults as a guide to the administrator. Local overrides can also be
created by creating drop-ins, as described below. The main configuration
file can also be edited for this purpose (or a copy in /etc/ if it is
shipped under /usr/), however using drop-ins for local configuration is
recommended over modifications to the main configuration file.
In addition to the main configuration file, drop-in configuration
snippets are read from /usr/lib/systemd/*.conf.d/,
/usr/local/lib/systemd/*.conf.d/, and /etc/systemd/*.conf.d/. Those
drop-ins have higher precedence and override the main configuration
file. Files in the *.conf.d/ configuration subdirectories are sorted by
their filename in lexicographic order, regardless of in which of the
subdirectories they reside. When multiple files specify the same option,
for options which accept just a single value, the entry in the file
sorted last takes precedence, and for options which accept a list of
values, entries are collected as they occur in the sorted files.
When packages need to customize the configuration, they can install
drop-ins under /usr/. Files in /etc/ are reserved for the local
administrator, who may use this logic to override the configuration
files installed by vendor packages. Drop-ins have to be used to override
package drop-ins, since the main configuration file has lower
precedence. It is recommended to prefix all filenames in those
subdirectories with a two-digit number and a dash, to simplify the
ordering. This also defines a concept of drop-in priorities to allow OS
vendors to ship drop-ins within a specific range lower than the range
used by users. This should lower the risk of package drop-ins overriding
accidentally drop-ins defined by users. It is recommended to use the
range 10-40 for drop-ins in /usr/ and the range 60-90 for drop-ins in
/etc/ and /run/, to make sure that local and transient drop-ins take
priority over drop-ins shipped by the OS vendor.
To disable a configuration file supplied by the vendor, the recommended
way is to place a symlink to /dev/null in the configuration directory in
/etc/, with the same filename as the vendor configuration file.
OPTIONS
All options are configured in the [IOCost] section:
TargetSolution=
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
IOCOST_SOLUTIONS is used instead.
E.g. "TargetSolution=isolated-bandwidth".
Added in version 254.
SEE ALSO
udevadm(8), The iocost-benchmarks github project[1], The resctl-bench
documentation details how the values are obtained[3]
NOTES
1. iocost-benchmark
https://github.com/iocost-benchmark/iocost-benchmarks
2. 💣💥🧨💥💥💣 Please note that those configuration files must be available
at all times. If /usr/local/ is a separate partition, it may not be
available during early boot, and must not be used for configuration.
3. The resctl-bench documentation details how the values are obtained
https://github.com/facebookexperimental/resctl-demo/tree/main/resctl-bench/doc
systemd 257.9 IOCOST.CONF(5)
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