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Documentation / block / switching-sched.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:00 EST.

1	To choose IO schedulers at boot time, use the argument 'elevator=deadline'.
2	'noop' and 'cfq' (the default) are also available. IO schedulers are assigned
3	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	
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 deadline 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 deadline [cfq]
35	# echo deadline > /sys/block/hda/queue/scheduler
36	# cat /sys/block/hda/queue/scheduler
37	noop [deadline] cfq
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