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>

1 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/block/switching-sched.txt b/Documentation/block/switching-sched.txt
index 5fa130a67531..634c952e1964 100644
--- a/Documentation/block/switching-sched.txt
+++ b/Documentation/block/switching-sched.txt
@@ -1,3 +1,18 @@
+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
@@ -20,3 +35,9 @@ 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