sched: Optimize build_sched_domains() for saving first SD node for a cpu

We are saving first scheduling domain for a cpu in build_sched_domains() by
iterating over the nested sd->child list. We don't actually need to do it this
way.

tl will be equal to sched_domain_topology for the first iteration and so we can
set *per_cpu_ptr(d.sd, i) based on that.  So, save pointer to first SD while
running the iteration loop over tl's.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/fc473527cbc4dfa0b8eeef2a59db74684eb59a83.1370436120.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 342e74419f8f..137dcc03f66d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5985,16 +5985,13 @@ static int build_sched_domains(const struct cpumask *cpu_map,
                 sd = NULL;
                 for (tl = sched_domain_topology; tl->init; tl++) {
                         sd = build_sched_domain(tl, cpu_map, attr, sd, i);
+                        if (tl == sched_domain_topology)
+                                *per_cpu_ptr(d.sd, i) = sd;
                         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)
-                        sd = sd->child;
-
-                *per_cpu_ptr(d.sd, i) = sd;
         }
 
         /* Build the groups for the domains */