[tip:sched/urgent] sched: Avoid creating superfluous NUMA domains on non-NUMA systems

From: tip-bot for Peter Zijlstra
Date: Wed Jul 20 2011 - 13:30:18 EST

Commit-ID: d110235d2c331c4f79e0879f51104be79e17a469
Gitweb: http://git.kernel.org/tip/d110235d2c331c4f79e0879f51104be79e17a469
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Wed, 20 Jul 2011 18:42:57 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Wed, 20 Jul 2011 18:54:33 +0200

sched: Avoid creating superfluous NUMA domains on non-NUMA systems

When creating sched_domains, stop when we've covered the entire
target span instead of continuing to create domains, only to
later find they're redundant and throw them away again.

This avoids single node systems from touching funny NUMA
sched_domain creation code and reduces the risks of the new

Requested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxx>
Cc: mahesh@xxxxxxxxxxxxxxxxxx
Cc: benh@xxxxxxxxxxxxxxxxxxx
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Link: 1311180177.29152.57.camel@twins">http://lkml.kernel.org/r/1311180177.29152.57.camel@twins
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
kernel/sched.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 921adf6..14168c4 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7436,6 +7436,8 @@ static int build_sched_domains(const struct cpumask *cpu_map,
sd = build_sched_domain(tl, &d, cpu_map, attr, sd, i);
if (tl->flags & SDTL_OVERLAP || sched_feat(FORCE_SD_OVERLAP))
sd->flags |= SD_OVERLAP;
+ if (cpumask_equal(cpu_map, sched_domain_span(sd)))
+ break;

while (sd->child)
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