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Subject[patch v3 4/6] sched, nohz: cleanup the find_new_ilb() using sched groups nr_busy_cpus
nr_busy_cpus in the sched_group_power indicates whether the group
is semi idle or not. This helps remove the is_semi_idle_group() and simplify
the find_new_ilb() in the context of finding an optimal cpu that can do
idle load balancing.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
kernel/sched/fair.c | 48 ++++++++++++------------------------------------
1 file changed, 12 insertions(+), 36 deletions(-)
Index: tip/kernel/sched/fair.c
===================================================================
--- tip.orig/kernel/sched/fair.c
+++ tip/kernel/sched/fair.c
@@ -4710,7 +4710,6 @@ out_unlock:
*/
static struct {
cpumask_var_t idle_cpus_mask;
- cpumask_var_t grp_idle_mask;
atomic_t nr_cpus;
unsigned long next_balance; /* in jiffy units */
} nohz ____cacheline_aligned;
@@ -4751,33 +4750,6 @@ static inline struct sched_domain *lowes
(sd && (sd->flags & flag)); sd = sd->parent)

/**
- * is_semi_idle_group - Checks if the given sched_group is semi-idle.
- * @ilb_group: group to be checked for semi-idleness
- *
- * Returns: 1 if the group is semi-idle. 0 otherwise.
- *
- * We define a sched_group to be semi idle if it has atleast one idle-CPU
- * and atleast one non-idle CPU. This helper function checks if the given
- * sched_group is semi-idle or not.
- */
-static inline int is_semi_idle_group(struct sched_group *ilb_group)
-{
- cpumask_and(nohz.grp_idle_mask, nohz.idle_cpus_mask,
- sched_group_cpus(ilb_group));
-
- /*
- * A sched_group is semi-idle when it has atleast one busy cpu
- * and atleast one idle cpu.
- */
- if (cpumask_empty(nohz.grp_idle_mask))
- return 0;
-
- if (cpumask_equal(nohz.grp_idle_mask, sched_group_cpus(ilb_group)))
- return 0;
-
- return 1;
-}
-/**
* find_new_ilb - Finds the optimum idle load balancer for nomination.
* @cpu: The cpu which is nominating a new idle_load_balancer.
*
@@ -4792,8 +4764,8 @@ static inline int is_semi_idle_group(str
static int find_new_ilb(int cpu)
{
int ilb = cpumask_first(nohz.idle_cpus_mask);
+ struct sched_group *ilbg;
struct sched_domain *sd;
- struct sched_group *ilb_group;

/*
* Have idle load balancer selection from semi-idle packages only
@@ -4811,23 +4783,28 @@ static int find_new_ilb(int cpu)

rcu_read_lock();
for_each_flag_domain(cpu, sd, SD_POWERSAVINGS_BALANCE) {
- ilb_group = sd->groups;
+ ilbg = sd->groups;

do {
- if (is_semi_idle_group(ilb_group)) {
- ilb = cpumask_first(nohz.grp_idle_mask);
+ if (ilbg->group_weight !=
+ atomic_read(&ilbg->sgp->nr_busy_cpus)) {
+ ilb = cpumask_first_and(nohz.idle_cpus_mask,
+ sched_group_cpus(ilbg));
goto unlock;
}

- ilb_group = ilb_group->next;
+ ilbg = ilbg->next;

- } while (ilb_group != sd->groups);
+ } while (ilbg != sd->groups);
}
unlock:
rcu_read_unlock();

out_done:
- return ilb;
+ if (ilb < nr_cpu_ids && idle_cpu(ilb))
+ return ilb;
+
+ return nr_cpu_ids;
}
#else /* (CONFIG_SCHED_MC || CONFIG_SCHED_SMT) */
static inline int find_new_ilb(int call_cpu)
@@ -5565,7 +5542,6 @@ __init void init_sched_fair_class(void)

#ifdef CONFIG_NO_HZ
zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
- alloc_cpumask_var(&nohz.grp_idle_mask, GFP_NOWAIT);
#endif
#endif /* SMP */




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