[net-next-2.6.git] / Documentation / block / switching-sched.txt

To choose IO schedulers at boot time, use the argument 'elevator=deadline'.
'noop', 'as' 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

As of the Linux 2.6.10 kernel, it is now possible to change the
IO scheduler for a given block device on the fly (thus making it possible,
for instance, to set the CFQ scheduler for the system default, but
set a specific device to use the anticipatory or noop 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/hda/queue/scheduler
noop anticipatory deadline [cfq]
# echo anticipatory > /sys/block/hda/queue/scheduler
# cat /sys/block/hda/queue/scheduler
noop [anticipatory] deadline cfq
Commit	Line	Data
23c76983 AB	1	To choose IO schedulers at boot time, use the argument 'elevator=deadline'.
	2	'noop', 'as' and 'cfq' (the default) are also available. IO schedulers are
	3	assigned globally at boot time only presently.
	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
73af994c VK	16	As of the Linux 2.6.10 kernel, it is now possible to change the
	17	IO scheduler for a given block device on the fly (thus making it possible,
	18	for instance, to set the CFQ scheduler for the system default, but
	19	set a specific device to use the anticipatory or noop schedulers - which
	20	can improve that device's throughput).
	21
	22	To set a specific scheduler, simply do this:
	23
	24	echo SCHEDNAME > /sys/block/DEV/queue/scheduler
	25
	26	where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
	27	device name (hda, hdb, sga, or whatever you happen to have).
	28
	29	The list of defined schedulers can be found by simply doing
	30	a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
	31	will be displayed, with the currently selected scheduler in brackets:
	32
	33	# cat /sys/block/hda/queue/scheduler
	34	noop anticipatory deadline [cfq]
	35	# echo anticipatory > /sys/block/hda/queue/scheduler
	36	# cat /sys/block/hda/queue/scheduler
	37	noop [anticipatory] deadline cfq