How To Change The IO Scheduling Class And Priority In Linux

This tutorial makes use of the Linux command-line program ionice.

Scheduling classes:

0. none:
1. real time: The hgihest-importantance schduling class. There are eight priorites (0-7), with lower numbers meaning higher priorites. This scheduling class cannot be assigned by a non-root user.
2. best effort: This class will be assigned to any process which didn’t explicitly assign a class.
3. idle: The process will only get disk time when no other non-idle process has requested disk access for a defined grace period. idle IO usage should no have impact on normal system activity.

To Get The IO Scheduling Class And Priority Of An Existing Process

Use the following command:

ionice -p <PID>

where <PID> is the process ID of the process you want to get the IO scheduling class and priority for. The command will return the IO scheduling class <class> and priority <prio> in the form:

<class>: prio <priority>

For example:

$ ionice -p 0
none: prio 4

Thus the process with PID=0 has a scheduling class of none and a priority of 4.

To Set The IO Scheduling Class And Priority Of An Existing Process

To change the IO scheduling class and priority for an already running process:

ionice -c <class> -n <class-priority> -p <PID>

To start a process and set the IO scheduling class and priority at the same time:

ionice -c <class> -n <class-priority> <COMMAND>

where <COMMAND> is standard command-line command + arguments. For example, to start a process running fstrim / with the lowest IO schdeduling class and lowest priority:

ionice -c 3 -n 7 fstrim /