dm mpath: add service time load balancer

This patch adds a service time oriented dynamic load balancer,
dm-service-time, which selects the path with the shortest estimated
service time for the incoming I/O.
The service time is estimated by dividing the in-flight I/O size
by a performance value of each path.

The performance value can be given as a table argument at the table
loading time.  If no performance value is given, all paths are
considered equal.

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, 10 insertions, 0 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 3b311d273346..09f93fa68912 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -258,6 +258,16 @@ config DM_MULTIPATH_QL
 
           If unsure, say N.
 
+config DM_MULTIPATH_ST
+        tristate "I/O Path Selector based on the service time"
+        depends on DM_MULTIPATH
+        ---help---
+          This path selector is a dynamic load balancer which selects
+          the path expected to complete the incoming I/O in the shortest
+          time.
+
+          If unsure, say N.
+
 config DM_DELAY
         tristate "I/O delaying target (EXPERIMENTAL)"
         depends on BLK_DEV_DM && EXPERIMENTAL