Use Average path priority value for path switching

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

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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>