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linux/Documentation/block/switching-sched.txt
Wang Sheng-Hui b31966816d Documentation: drop as block elevator reference in switching-sched.txt
Remove 'as' for as is no longer supported, and we can not use
'elevator=as' any more.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-11-04 12:01:48 -07:00

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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
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 deadline 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 deadline [cfq]
# echo deadline > /sys/block/hda/queue/scheduler
# cat /sys/block/hda/queue/scheduler
noop [deadline] cfq