linux-kernel - [PATCH v7 3/8] sched: favour lower logical cpu number for sched

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Message-ID: <20081218175615.29812.70736.stgit@drishya.in.ibm.com>
Date:	Thu, 18 Dec 2008 23:26:16 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	David Collier-Brown <davecb@....com>,
	Tim Connors <tconnors@...ro.swin.edu.au>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Pavel Machek <pavel@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: [PATCH v7 3/8] sched: favour lower logical cpu number for sched_mc
	balance

Just in case two groups have identical load, prefer to move load to lower
logical cpu number rather than the present logic of moving to higher logical
number.

find_busiest_group() tries to look for a group_leader that has spare capacity
to take more tasks and freeup an appropriate least loaded group.  Just in case
there is a tie and the load is equal, then the group with higher logical number
is favoured.  This conflicts with user space irqbalance daemon that will move
interrupts to lower logical number if the system utilisation is very low.

Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
---

 kernel/sched.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 16897ab..0b9bbbd 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3264,7 +3264,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 		 */
 		if ((sum_nr_running < min_nr_running) ||
 		    (sum_nr_running == min_nr_running &&
-		     first_cpu(group->cpumask) <
+		     first_cpu(group->cpumask) >
 		     first_cpu(group_min->cpumask))) {
 			group_min = group;
 			min_nr_running = sum_nr_running;
@@ -3280,7 +3280,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 		if (sum_nr_running <= group_capacity - 1) {
 			if (sum_nr_running > leader_nr_running ||
 			    (sum_nr_running == leader_nr_running &&
-			     first_cpu(group->cpumask) >
+			     first_cpu(group->cpumask) <
 			      first_cpu(group_leader->cpumask))) {
 				group_leader = group;
 				leader_nr_running = sum_nr_running;

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