linux/Documentation/block/switching-sched.txt
Alan D. Brunelle 23c76983e2 Some IO scheduler cleanup in Documentation/block
as-iosched.txt:
  o  Changed IO scheduler selection text to a reference to the
     switching-sched.txt file.

  o  Fixed typo: 'for up time...' -> 'for up to...'

  o  Added short description of the est_time file.

deadline-iosched.txt:
  o  Changed IO scheduler selection text to a reference to the
     switching-sched.txt file.

  o  Removed references to non-existent seek-cost and stream_unit.

  o  Fixed typo: 'write_starved' -> 'writes_starved'

switching-sched.txt:
  o  Added in boot-time argument to set the default IO scheduler. (From
     as-iosched.txt)

  o  Added in sysfs mount instructions. (From deadline-iosched.txt)

Signed-off-by: Alan D. Brunelle <Alan.Brunelle@hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2007-10-16 09:59:55 +02:00

44 lines
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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
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