dm mpath: add queue length load balancer

This patch adds a dynamic load balancer, dm-queue-length, which
balances the number of in-flight I/Os across the paths.

The code is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 36e0675be9f7..3b311d273346 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -249,6 +249,15 @@ config DM_MULTIPATH
         ---help---
           Allow volume managers to support multipath hardware.
 
+config DM_MULTIPATH_QL
+        tristate "I/O Path Selector based on the number of in-flight I/Os"
+        depends on DM_MULTIPATH
+        ---help---
+          This path selector is a dynamic load balancer which selects
+          the path with the least number of in-flight I/Os.
+
+          If unsure, say N.
+
 config DM_DELAY
         tristate "I/O delaying target (EXPERIMENTAL)"
         depends on BLK_DEV_DM && EXPERIMENTAL