linux-kernel - [PATCH] sched:make ads.avg

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Date:	Fri, 15 Apr 2011 10:11:37 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org
Cc:	tim.c.chen@...el.com, suresh.b.siddha@...el.com
Subject: [PATCH] sched:make ads.avg_load update in time

commit 866ab43efd325fae cause hackbench benchmark process mode
performance dropping about 15% on our x86_64 machines. The patch works
as its origin purpose, but it cause nearly double context switch on
hackbench running.  The sds.avg_load was not updated in time cause this.
So when move the sds.avg_load update before group_imb checking,
performance recovered totally.

Signed-off-by: Alex Shi <alex.shi@...el.com>
---
 kernel/sched_fair.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 7f00772..036b660 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3127,6 +3127,8 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 	if (!sds.busiest || sds.busiest_nr_running == 0)
 		goto out_balanced;
 
+	sds->avg_load = (SCHED_LOAD_SCALE * sds->total_load) / sds->total_pwr;
+
 	/*
 	 * If the busiest group is imbalanced the below checks don't
 	 * work because they assumes all things are equal, which typically
@@ -3151,7 +3153,6 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 	 * Don't pull any tasks if this group is already above the domain
 	 * average load.
 	 */
-	sds.avg_load = (SCHED_LOAD_SCALE * sds.total_load) / sds.total_pwr;
 	if (sds.this_load >= sds.avg_load)
 		goto out_balanced;
 
-- 
1.7.0

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