Switching Scheduler

Each io queue has a set of io scheduler tunables associated with it. These tunables control how the io scheduler works. You can find these entries in:

/sys/block/<device>/queue/iosched

assuming that you have sysfs mounted on /sys. If you don’t have sysfs mounted, you can do so by typing:

# mount none /sys -t sysfs

It is possible to change the IO scheduler for a given block device on the fly to select one of mq-deadline, none, bfq, or kyber schedulers - which can improve that device’s throughput.

To set a specific scheduler, simply do this:

echo SCHEDNAME > /sys/block/DEV/queue/scheduler

where SCHEDNAME is the name of a defined IO scheduler, and DEV is the device name (hda, hdb, sga, or whatever you happen to have).

The list of defined schedulers can be found by simply doing a “cat /sys/block/DEV/queue/scheduler” - the list of valid names will be displayed, with the currently selected scheduler in brackets:

# cat /sys/block/sda/queue/scheduler
[mq-deadline] kyber bfq none
# echo none >/sys/block/sda/queue/scheduler
# cat /sys/block/sda/queue/scheduler
[none] mq-deadline kyber bfq