path: root/Documentation/block/switching-sched.txt
diff options
Diffstat (limited to 'Documentation/block/switching-sched.txt')
1 files changed, 37 insertions, 0 deletions
diff --git a/Documentation/block/switching-sched.txt b/Documentation/block/switching-sched.txt
new file mode 100644
index 00000000..3b2612e3
--- /dev/null
+++ b/Documentation/block/switching-sched.txt
@@ -0,0 +1,37 @@
+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
+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