[PATCH 3/3] sched: Fix sd_parent_degenerate for SD_POWERSAVINGS_BALANCE.

[Gautham R Shenoy <ego@in.ibm.com>]

Currently a sched_domain having a single group can be prevented from getting
degenerated if it contains a SD_POWERSAVINGS_BALANCE flag. But since it has
only one group, it won't have any scope for performing powersavings balance as
it does not have a sibling group to pull from.

Apart from not provide any powersavings, it also fails to participate
in normal load-balancing.

Fix this by allowing such a sched_domain to degenerate and pass on the
responsibility of performing the POWERSAVINGS_BALANCE to it's parent domain.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
---

 kernel/sched.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index af88f5a..32858fd 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6934,6 +6934,17 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 				SD_SHARE_PKG_RESOURCES);
 		if (nr_node_ids == 1)
 			pflags &= ~SD_SERIALIZE;
+
+		/*
+		 * If the only flag that is preventing us from degenerating
+		 * a domain with a single group is power_savings balance,
+		 * see if we can transfer that responsibility to the new parent
+		 */
+		if (pflags & SD_POWERSAVINGS_BALANCE && parent->parent) {
+			pflags &= ~SD_POWERSAVINGS_BALANCE;
+			parent->parent->flags |=
+				sd_power_saving_flags(parent->level);
+		}
 	}
 	if (~cflags & pflags)
 		return 0;