linux-kernel - [PATCH] sched: Call update_group_power only for local

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Date:	Thu,  1 Jul 2010 16:12:22 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Venkatesh Pallipadi <venki@...gle.com>
Subject: [PATCH] sched: Call update_group_power only for local_group

commit 871e35b moved update_group_power() call in update_sg_lb_stats(),
resulting in it being called for each group, even though it only updates
the power of local group. As a result we have frequent redundant
update_group_power() calls.

Move it back under "if (local_group)" condition.

This reduces the number of calls to update_group_power by a factor of 4
on my 4 core in 4 NUMA nodes test system.

Signed-off-by: Venkatesh Pallipadi <venki@...gle.com>
---
 kernel/sched_fair.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index a878b53..369d53d 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2359,8 +2359,11 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 	unsigned int balance_cpu = -1, first_idle_cpu = 0;
 	unsigned long avg_load_per_task = 0;
 
-	if (local_group)
+	if (local_group) {
 		balance_cpu = group_first_cpu(group);
+		update_group_power(sd, this_cpu);
+	}
+
 
 	/* Tally up the load of all CPUs in the group */
 	max_cpu_load = 0;
@@ -2406,8 +2409,6 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 		return;
 	}
 
-	update_group_power(sd, this_cpu);
-
 	/* Adjust by relative CPU power of the group */
 	sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;
 
-- 
1.7.1

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