Use Average path priority value for path switching

Hi Christophe,

I submitted this patch on Jul 2
(http://marc.info/?l=dm-devel&m=124658334721911&w=2). Resending it.

Only change is a field name from up_paths to enabled_paths.

Hi Hannes,

Need an ACK from you :-).

regards,

chandra

-----------------------------------------------------------------------
Failback happens only when the sum of priorities of all paths
(on the higher priority path group) is greater than the sum
of priorities of all paths on the lower priority path group.

This leads into problems when there are more than one paths
in each of the path groups, and the sum of all paths in the
lower priority path group is greater than that of path priority
of a single high priority path.

This patch fixes the problem by using average priority of
the path group to decide on which path group to switch over.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>

diff --git a/libmultipath/structs.h b/libmultipath/structs.h
index aafadbae99b2951715c7d0c650d02b4985a66849..afd124662bef6581d7dff9f5e31a110433e9693f 100644 (file)
--- a/libmultipath/structs.h
+++ b/libmultipath/structs.h
@@ -202,6 +202,7 @@ struct pathgroup {
        long id;
        int status;
        int priority;
+       int enabled_paths;
        vector paths;
        char * selector;
 };

diff --git a/libmultipath/switchgroup.c b/libmultipath/switchgroup.c
index 5d6e80500d3ca4331dd181b417c257636274d834..f62c558b83af54a8c1fee355eb8ecb21e7cd1ded 100644 (file)
--- a/libmultipath/switchgroup.c
+++ b/libmultipath/switchgroup.c
@@ -14,13 +14,16 @@ path_group_prio_update (struct pathgroup * pgp)
        int priority = 0;
        struct path * pp;
 
+       pgp->enabled_paths = 0;
        if (!pgp->paths) {
                pgp->priority = 0;
                return;
        }
        vector_foreach_slot (pgp->paths, pp, i) {
-               if (pp->state != PATH_DOWN)
+               if (pp->state != PATH_DOWN) {
                        priority += pp->priority;
+                       pgp->enabled_paths++;
+               }
        }
        pgp->priority = priority;
 }
@@ -29,8 +32,9 @@ extern int
 select_path_group (struct multipath * mpp)
 {
        int i;
-       int highest = 0;
+       int max_priority = 0, avg_priority;
        int bestpg = 1;
+       int max_enabled_paths = 1;
        struct pathgroup * pgp;
 
        if (!mpp->pg)
@@ -41,9 +45,18 @@ select_path_group (struct multipath * mpp)
                        continue;
 
                path_group_prio_update(pgp);
-               if (pgp->priority > highest) {
-                       highest = pgp->priority;
-                       bestpg = i + 1;
+               if (pgp->enabled_paths) {
+                       avg_priority = pgp->priority / pgp->enabled_paths;
+                       if (avg_priority > max_priority) {
+                               max_priority = avg_priority;
+                               max_enabled_paths = pgp->enabled_paths;
+                               bestpg = i + 1;
+                       } else if (avg_priority == max_priority) {
+                               if (pgp->enabled_paths > max_enabled_paths) {
+                                       max_enabled_paths = pgp->enabled_paths;
+                                       bestpg = i + 1;
+                               }
+                       }
                }
        }
        return bestpg;