[PATCH 1/2] sched: Optimize build_sched_domains() for saving first SD node for a cpu

From: Viresh Kumar
Date: Tue Jun 04 2013 - 07:20:52 EST

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

*per_cpu_ptr(d.sd, i) is guaranteed to be NULL in the beginning as we have
called __visit_domain_allocation_hell() which does a memset to zero for struct

So, save pointer to first SD while running the iteration loop over tl's.

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
kernel/sched/core.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 58453b8..638f6cb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6533,16 +6533,13 @@ 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, &d, cpu_map, attr, sd, i);
+ if (!*per_cpu_ptr(d.sd, i))
+ *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)))
- while (sd->child)
- sd = sd->child;
- *per_cpu_ptr(d.sd, i) = sd;

/* Build the groups for the domains */

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