summaryrefslogtreecommitdiff
path: root/Documentation/block/as-iosched.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/block/as-iosched.txt')
-rw-r--r--Documentation/block/as-iosched.txt21
1 files changed, 13 insertions, 8 deletions
diff --git a/Documentation/block/as-iosched.txt b/Documentation/block/as-iosched.txt
index a598fe10a297..738b72be128e 100644
--- a/Documentation/block/as-iosched.txt
+++ b/Documentation/block/as-iosched.txt
@@ -20,15 +20,10 @@ actually has a head for each physical device in the logical RAID device.
However, setting the antic_expire (see tunable parameters below) produces
very similar behavior to the deadline IO scheduler.
-
Selecting IO schedulers
-----------------------
-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. It's also possible to change
-the IO scheduler for a determined device on the fly, as described in
-Documentation/block/switching-sched.txt.
-
+Refer to Documentation/block/switching-sched.txt for information on
+selecting an io scheduler on a per-device basis.
Anticipatory IO scheduler Policies
----------------------------------
@@ -115,7 +110,7 @@ statistics (average think time, average seek distance) on the process
that submitted the just completed request are examined. If it seems
likely that that process will submit another request soon, and that
request is likely to be near the just completed request, then the IO
-scheduler will stop dispatching more read requests for up time (antic_expire)
+scheduler will stop dispatching more read requests for up to (antic_expire)
milliseconds, hoping that process will submit a new request near the one
that just completed. If such a request is made, then it is dispatched
immediately. If the antic_expire wait time expires, then the IO scheduler
@@ -165,3 +160,13 @@ The parameters are:
for big seek time devices though not a linear correspondence - most
processes have only a few ms thinktime.
+In addition to the tunables above there is a read-only file named est_time
+which, when read, will show:
+
+ - The probability of a task exiting without a cooperating task
+ submitting an anticipated IO.
+
+ - The current mean think time.
+
+ - The seek distance used to determine if an incoming IO is better.
+