Chapter 11. Setting the disk scheduler

Procedure

1. Optional: Select an existing TuneD profile on which your profile will be based. For a list of available profiles, see TuneD profiles distributed with RHEL.

   To see which profile is currently active, use:

   $ tuned-adm active

2. Create a new directory to hold your TuneD profile:

   # mkdir /etc/tuned/my-profile

3. Find the system unique identifier of the selected block device:

   $ udevadm info --query=property --name=/dev/device | grep -E '(WWN|SERIAL)'
   
   ID_WWN=0x5002538d00000000_
   ID_SERIAL=Generic-_SD_MMC_20120501030900000-0:0
   ID_SERIAL_SHORT=20120501030900000

   Note

   The command in the this example will return all values identified as a World Wide Name (WWN) or serial number associated with the specified block device. Although it is preferred to use a WWN, the WWN is not always available for a given device and any values returned by the example command are acceptable to use as the device system unique ID.

4. Create the /etc/tuned/my-profile/tuned.conf configuration file. In the file, set the following options:

   1. Optional: Include an existing profile:

      [main]
      include=existing-profile

   2. Set the selected disk scheduler for the device that matches the WWN identifier:

      [disk]
      devices_udev_regex=IDNAME=device system unique id
      elevator=selected-scheduler

      Here:

      • Replace IDNAME with the name of the identifier being used (for example, ID_WWN).

      • Replace device system unique id with the value of the chosen identifier (for example, 0x5002538d00000000).

        To match multiple devices in the devices_udev_regex option, enclose the identifiers in parentheses and separate them with vertical bars:

        devices_udev_regex=(ID_WWN=0x5002538d00000000)|(ID_WWN=0x1234567800000000)

5. Enable your profile:

   # tuned-adm profile my-profile

Verification

1. Verify that the TuneD profile is active and applied:

   $ tuned-adm active
   
   Current active profile: my-profile

   $ tuned-adm verify
   
   Verification succeeded, current system settings match the preset profile.
   See TuneD log file ('/var/log/tuned/tuned.log') for details.

2. Read the contents of the /sys/block/device/queue/scheduler file:

   # cat /sys/block/device/queue/scheduler
   
   [mq-deadline] kyber bfq none

   In the file name, replace device with the block device name, for example sdc.

   The active scheduler is listed in square brackets ([]).

Procedure

1. Find the system unique identifier of the block device:

   $ udevadm info --name=/dev/device | grep -E '(WWN|SERIAL)'
   E: ID_WWN=0x5002538d00000000
   E: ID_SERIAL=Generic-_SD_MMC_20120501030900000-0:0
   E: ID_SERIAL_SHORT=20120501030900000

   Note

   The command in the this example will return all values identified as a World Wide Name (WWN) or serial number associated with the specified block device. Although it is preferred to use a WWN, the WWN is not always available for a given device and any values returned by the example command are acceptable to use as the device system unique ID.

2. Configure the udev rule. Create the /etc/udev/rules.d/99-scheduler.rules file with the following content:

   ACTION=="add|change", SUBSYSTEM=="block", ENV{IDNAME}=="device system unique id", ATTR{queue/scheduler}="selected-scheduler"

   Here:

   • Replace IDNAME with the name of the identifier being used (for example, ID_WWN).
   • Replace device system unique id with the value of the chosen identifier (for example, 0x5002538d00000000).

3. Reload udev rules:

   # udevadm control --reload-rules

4. Apply the scheduler configuration:

   # udevadm trigger --type=devices --action=change