[deliverable/linux.git] / Documentation / block / switching-sched.txt

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
73af994c VK	1	As of the Linux 2.6.10 kernel, it is now possible to change the
	2	IO scheduler for a given block device on the fly (thus making it possible,
	3	for instance, to set the CFQ scheduler for the system default, but
	4	set a specific device to use the anticipatory or noop schedulers - which
	5	can improve that device's throughput).
	6
	7	To set a specific scheduler, simply do this:
	8
	9	echo SCHEDNAME > /sys/block/DEV/queue/scheduler
	10
	11	where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
	12	device name (hda, hdb, sga, or whatever you happen to have).
	13
	14	The list of defined schedulers can be found by simply doing
	15	a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
	16	will be displayed, with the currently selected scheduler in brackets:
	17
	18	# cat /sys/block/hda/queue/scheduler
	19	noop anticipatory deadline [cfq]
	20	# echo anticipatory > /sys/block/hda/queue/scheduler
	21	# cat /sys/block/hda/queue/scheduler
	22	noop [anticipatory] deadline cfq