nr_busy_cpus parameter is used by nohz_kick_needed() to find out the number
of busy cpus in a sched domain which has SD_SHARE_PKG_RESOURCES flag set.
Therefore instead of updating nr_busy_cpus at every level of sched domain,
since it is irrelevant, we can update this parameter only at the parent
domain of the sd which has this flag set. Introduce a per-cpu parameter
sd_busy which represents this parent domain.

In nohz_kick_needed() we directly query the nr_busy_cpus parameter
associated with the groups of sd_busy.

By associating sd_busy with the highest domain which has
SD_SHARE_PKG_RESOURCES flag set, we cover all lower level domains which could
have this flag set and trigger nohz_idle_balancing if any of the levels have
more than one busy cpu.

sd_busy is irrelevant for asymmetric load balancing. However sd_asym has been
introduced to represent the highest sched domain which has SD_ASYM_PACKING flag set
so that it can be queried directly when required.

While we are at it, we might as well change the nohz_idle parameter to be
updated at the sd_busy domain level alone and not the base domain level of a CPU.
This will unify the concept of busy cpus at just one level of sched domain
where it is currently used.

Signed-off-by: Preeti U Murthy<redacted>
---
 kernel/sched/core.c  |    6 ++++++
 kernel/sched/fair.c  |   38 ++++++++++++++++++++------------------
 kernel/sched/sched.h |    2 ++
 3 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c06b8d3..e6a6244 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c

@@ -5271,6 +5271,8 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc);
 DEFINE_PER_CPU(int, sd_llc_size);
 DEFINE_PER_CPU(int, sd_llc_id);
 DEFINE_PER_CPU(struct sched_domain *, sd_numa);
+DEFINE_PER_CPU(struct sched_domain *, sd_busy);
+DEFINE_PER_CPU(struct sched_domain *, sd_asym);

 static void update_top_cache_domain(int cpu)
 {

@@ -5282,6 +5284,7 @@ static void update_top_cache_domain(int cpu)
 	if (sd) {
 		id = cpumask_first(sched_domain_span(sd));
 		size = cpumask_weight(sched_domain_span(sd));
+		rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent);
 	}