linux-kernel - [PATCH v2] sched: update_top_cache_domain only at the times of building sched domain.

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Date:	Tue, 23 Jul 2013 23:42:12 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	mingo@...nel.org, peterz@...radead.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH v2] sched: update_top_cache_domain only at the times of
 building sched domain.

Currently, update_top_cache_domain() is called whenever schedule domain is built or destroyed. But, the following
callpath shows that they're at the same callpath and can be avoided update_top_cache_domain() while destroying schedule
domain and update only at the times of building schedule domains.

	partition_sched_domains()
		detach_destroy_domain()
			cpu_attach_domain()
				update_top_cache_domain()
		build_sched_domains()
			cpu_attach_domain()
				update_top_cache_domain()

Changes since v1: use sd to determine when to skip, courtesy PeterZ

Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b7c32cb..387fb66 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5138,7 +5138,8 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 	rcu_assign_pointer(rq->sd, sd);
 	destroy_sched_domains(tmp, cpu);

-	update_top_cache_domain(cpu);
+	if (sd)
+		update_top_cache_domain(cpu);
 }

 /* cpus with isolated domains */

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