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Subject[109/123] sched: Pre-compute cpumask_weight(sched_domain_span(sd))
From: Peter Zijlstra <a.p.zijlstra@chello.nl>

commit 669c55e9f99b90e46eaa0f98a67ec53d46dc969a upstream

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@davemloft.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
include/linux/sched.h | 1 +
kernel/sched.c | 7 +++++--
kernel/sched_fair.c | 8 +++-----
3 files changed, 9 insertions(+), 7 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1000,6 +1000,7 @@ struct sched_domain {
char *name;
#endif

+ unsigned int span_weight;
/*
* Span of all CPUs in this domain.
*
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3678,7 +3678,7 @@ unsigned long __weak arch_scale_freq_pow

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;
@@ -3711,7 +3711,7 @@ 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;

@@ -8166,6 +8166,9 @@ cpu_attach_domain(struct sched_domain *s
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;
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1520,9 +1520,7 @@ select_task_rq_fair(struct rq *rq, struc
* 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) {
@@ -1566,10 +1564,10 @@ select_task_rq_fair(struct rq *rq, struc

/* 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;



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