[tip:sched/core] sched: Pre-compute cpumask_weight(sched_domain_span(sd))

[tip-bot for Peter Zijlstra]

Commit-ID:  669c55e9f99b90e46eaa0f98a67ec53d46dc969a
Gitweb:     http://git.kernel.org/tip/669c55e9f99b90e46eaa0f98a67ec53d46dc969a
Author:     Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Fri, 16 Apr 2010 14:59:29 +0200
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Fri, 23 Apr 2010 11:02:02 +0200

sched: Pre-compute cpumask_weight(sched_domain_span(sd))

Dave reported that his large SPARC machines spend lots of time in
hweight64(), try and optimize some of those needless cpumask_weight()
invocations (esp. with the large offstack cpumasks these are very
expensive indeed).

Reported-by: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 include/linux/sched.h |    1 +
 kernel/sched.c        |    3 +++
 kernel/sched_fair.c   |   12 +++++-------
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e3e900f..dfea405 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -960,6 +960,7 @@ struct sched_domain {
 	char *name;
 #endif
 
+	unsigned int span_weight;
 	/*
 	 * Span of all CPUs in this domain.
 	 *
diff --git a/kernel/sched.c b/kernel/sched.c
index 0cc913a..4956ed0 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6271,6 +6271,9 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 	struct rq *rq = cpu_rq(cpu);
 	struct sched_domain *tmp;
 
+	for (tmp = sd; tmp; tmp = tmp->parent)
+		tmp->span_weight = cpumask_weight(sched_domain_span(tmp));
+
 	/* Remove the sched domains which do not contribute to scheduling. */
 	for (tmp = sd; tmp; ) {
 		struct sched_domain *parent = tmp->parent;
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 88d3053..0a413c7 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1508,9 +1508,7 @@ select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_
 		 * Pick the largest domain to update shares over
 		 */
 		tmp = sd;
-		if (affine_sd && (!tmp ||
-				  cpumask_weight(sched_domain_span(affine_sd)) >
-				  cpumask_weight(sched_domain_span(sd))))
+		if (affine_sd && (!tmp || affine_sd->span_weight > sd->span_weight))
 			tmp = affine_sd;
 
 		if (tmp) {
@@ -1554,10 +1552,10 @@ select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_
 
 		/* Now try balancing at a lower domain level of new_cpu */
 		cpu = new_cpu;
-		weight = cpumask_weight(sched_domain_span(sd));
+		weight = sd->span_weight;
 		sd = NULL;
 		for_each_domain(cpu, tmp) {
-			if (weight <= cpumask_weight(sched_domain_span(tmp)))
+			if (weight <= tmp->span_weight)
 				break;
 			if (tmp->flags & sd_flag)
 				sd = tmp;
@@ -2243,7 +2241,7 @@ unsigned long __weak arch_scale_freq_power(struct sched_domain *sd, int cpu)
 
 unsigned long default_scale_smt_power(struct sched_domain *sd, int cpu)
 {
-	unsigned long weight = cpumask_weight(sched_domain_span(sd));
+	unsigned long weight = sd->span_weight;
 	unsigned long smt_gain = sd->smt_gain;
 
 	smt_gain /= weight;
@@ -2276,7 +2274,7 @@ unsigned long scale_rt_power(int cpu)
 
 static void update_cpu_power(struct sched_domain *sd, int cpu)
 {
-	unsigned long weight = cpumask_weight(sched_domain_span(sd));
+	unsigned long weight = sd->span_weight;
 	unsigned long power = SCHED_LOAD_SCALE;
 	struct sched_group *sdg = sd->groups;
 
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