linux-kernel - [tip:sched/core] sched: Avoid SMT siblings in select_idle

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Date:	Fri, 18 Nov 2011 15:40:42 -0800
From:	tip-bot for Peter Zijlstra <peterz@...radead.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, efault@....de, peterz@...radead.org,
	suresh.b.siddha@...el.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/core] sched: Avoid SMT siblings in select_idle_sibling() if possible

Commit-ID:  4dcfe1025b513c2c1da5bf5586adb0e80148f612
Gitweb:     http://git.kernel.org/tip/4dcfe1025b513c2c1da5bf5586adb0e80148f612
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Thu, 10 Nov 2011 13:01:10 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 16 Nov 2011 08:43:43 +0100

sched: Avoid SMT siblings in select_idle_sibling() if possible

Avoid select_idle_sibling() from picking a sibling thread if there's
an idle core that shares cache.

This fixes SMT balancing in the increasingly common case where there's
a shared cache core available to balance to.

Tested-by: Mike Galbraith <efault@....de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Suresh Siddha <suresh.b.siddha@...el.com>
Link: http://lkml.kernel.org/r/1321350377.1421.55.camel@twins
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_fair.c |   42 ++++++++++++++++++++++++++++--------------
 1 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 7e51b5b..ba0e1f4 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2326,7 +2326,8 @@ static int select_idle_sibling(struct task_struct *p, int target)
 	int cpu = smp_processor_id();
 	int prev_cpu = task_cpu(p);
 	struct sched_domain *sd;
-	int i;
+	struct sched_group *sg;
+	int i, smt = 0;
 
 	/*
 	 * If the task is going to be woken-up on this cpu and if it is
@@ -2346,25 +2347,38 @@ static int select_idle_sibling(struct task_struct *p, int target)
 	 * Otherwise, iterate the domains and find an elegible idle cpu.
 	 */
 	rcu_read_lock();
+again:
 	for_each_domain(target, sd) {
-		if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
-			break;
+		if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
+			continue;
 
-		for_each_cpu_and(i, sched_domain_span(sd), tsk_cpus_allowed(p)) {
-			if (idle_cpu(i)) {
-				target = i;
-				break;
+		if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
+			if (!smt) {
+				smt = 1;
+				goto again;
 			}
+			break;
 		}
 
-		/*
-		 * Lets stop looking for an idle sibling when we reached
-		 * the domain that spans the current cpu and prev_cpu.
-		 */
-		if (cpumask_test_cpu(cpu, sched_domain_span(sd)) &&
-		    cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))
-			break;
+		sg = sd->groups;
+		do {
+			if (!cpumask_intersects(sched_group_cpus(sg),
+						tsk_cpus_allowed(p)))
+				goto next;
+
+			for_each_cpu(i, sched_group_cpus(sg)) {
+				if (!idle_cpu(i))
+					goto next;
+			}
+
+			target = cpumask_first_and(sched_group_cpus(sg),
+					tsk_cpus_allowed(p));
+			goto done;
+next:
+			sg = sg->next;
+		} while (sg != sd->groups);
 	}
+done:
 	rcu_read_unlock();
 
 	return target;
--
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