linux-kernel - [tip:sched/core] sched: Reduce update_group

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Date:	Sat, 17 Jul 2010 11:12:19 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, suresh.b.siddha@...el.com,
	tglx@...utronix.de, venki@...gle.com, mingo@...e.hu
Subject: [tip:sched/core] sched: Reduce update_group_power() calls

Commit-ID:  bbc8cb5baead9607309583b20873ab0cc8d89eaf
Gitweb:     http://git.kernel.org/tip/bbc8cb5baead9607309583b20873ab0cc8d89eaf
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Fri, 9 Jul 2010 15:15:43 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sat, 17 Jul 2010 12:05:14 +0200

sched: Reduce update_group_power() calls

Currently we update cpu_power() too often, update_group_power() only
updates the local group's cpu_power but it gets called for all groups.

Furthermore, CPU_NEWLY_IDLE invocations will result in all cpus
calling it, even though a slow update of cpu_power is sufficient.

Therefore move the update under 'idle != CPU_NEWLY_IDLE &&
local_group' to reduce superfluous invocations.

Reported-by: Venkatesh Pallipadi <venki@...gle.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>
LKML-Reference: <1278612989.1900.176.camel@...top>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_fair.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e44a591..c9ac097 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2425,14 +2425,14 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 	 * domains. In the newly idle case, we will allow all the cpu's
 	 * to do the newly idle load balance.
 	 */
-	if (idle != CPU_NEWLY_IDLE && local_group &&
-	    balance_cpu != this_cpu) {
-		*balance = 0;
-		return;
+	if (idle != CPU_NEWLY_IDLE && local_group) {
+		if (balance_cpu != this_cpu) {
+			*balance = 0;
+			return;
+		}
+		update_group_power(sd, this_cpu);
 	}
 
-	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;
 
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