Documentation/block/switching-sched.rst
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::
[mq-deadline] kyber bfq none
[none] mq-deadline kyber bfq