sched: fix sd_parent_degenerate on non-numa smp machine

Impact: optimize the sched domains tree some more

The addition of SD_SERIALIZE flag added to SD_NODE_INIT prevented top level
dummy numa sched_domain to be properly degenerated on non-numa smp machine.
The reason is that in sd_parent_degenerate(), it found that the child and
parent does not have comon sched_domain flags due to SD_SERIALIZE.  However,
for non-numa smp box, the top level is a dummy with a single sched_group.

Filter out SD_SERIALIZE if it is on non-numa machine to properly degenerate
top level node sched_domain.  this will cut back some of the sd domain walk
in the load balancer code.

Signed-off-by: Ken Chen <kenchen@google.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 152828239ef01fb6d16adf43ee7718bf41574bdc..74498c840f933e7a1c63dd7ffb8e8db270e2bc34 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6768,6 +6768,8 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
                                SD_BALANCE_EXEC |
                                SD_SHARE_CPUPOWER |
                                SD_SHARE_PKG_RESOURCES);
+               if (nr_node_ids == 1)
+                       pflags &= ~SD_SERIALIZE;
        }
        if (~cflags & pflags)
                return 0;