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
SD_OVERLAP code.

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Anton Blanchard <anton@samba.org>
Cc: mahesh@linux.vnet.ibm.com
Cc: benh@kernel.crashing.org
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1311180177.29152.57.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 921adf6f6fad1d4cc7c29522af51abce83cfea97..14168c49a15428880f5b66702e12134eff4ba1fa 100644 (file)
--- 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)