[PATCH] 2.6.16 Block I/O Schedulers - document runtime selection

[Valdis.Kletnieks@vt.edu]

On Sun, 26 Mar 2006 22:19:52 PST, "Randy.Dunlap" said:

> Patches accepted... Please summarize what you have found, even if not in
> patch format (and I'll make it a patch).

From: Valdis Kletnieks <valdis.kletnieks@vt.edu>

We added the ability to change a block device's IO elevator scheduler both
at kernel boot and on-the-fly, but we only documented the elevator= boot
parameter.  Add a quick how-to on doing it on the fly.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
---
--- linux-2.6.16-mm1/Documentation/block/switching-sched.txt.new	2006-03-27 03:26:25.000000000 -0500
+++ linux-2.6.16-mm1/Documentation/block/switching-sched.txt	2006-03-27 03:33:39.000000000 -0500
@@ -0,0 +1,22 @@
+As of the Linux 2.6.mumble 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

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