[mirror_ubuntu-jammy-kernel.git] / Documentation / block / switching-sched.txt

To choose IO schedulers at boot time, use the argument 'elevator=deadline'.
'noop' and 'cfq' (the default) are also available. IO schedulers are assigned
globally at boot time only presently.

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
Commit	Line	Data
23c76983	1	To choose IO schedulers at boot time, use the argument 'elevator=deadline'.
b3196681 WSH	2	'noop' and 'cfq' (the default) are also available. IO schedulers are assigned
b3196681 WSH	3	globally at boot time only presently.
23c76983 AB	4
	5	Each io queue has a set of io scheduler tunables associated with it. These
	6	tunables control how the io scheduler works. You can find these entries
	7	in:
	8
	9	/sys/block/<device>/queue/iosched
	10
	11	assuming that you have sysfs mounted on /sys. If you don't have sysfs mounted,
	12	you can do so by typing:
	13
	14	# mount none /sys -t sysfs
	15
8614b008 AH	16	It is possible to change the IO scheduler for a given block device on
	17	the fly to select one of mq-deadline, none, bfq, or kyber schedulers -
	18	which can improve that device's throughput.
73af994c VK	19
	20	To set a specific scheduler, simply do this:
	21
	22	echo SCHEDNAME > /sys/block/DEV/queue/scheduler
	23
	24	where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
	25	device name (hda, hdb, sga, or whatever you happen to have).
	26
	27	The list of defined schedulers can be found by simply doing
	28	a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
	29	will be displayed, with the currently selected scheduler in brackets:
	30
8614b008 AH	31	# cat /sys/block/sda/queue/scheduler
	32	[mq-deadline] kyber bfq none
	33	# echo none >/sys/block/sda/queue/scheduler
	34	# cat /sys/block/sda/queue/scheduler
	35	[none] mq-deadline kyber bfq