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Subject[PATCHv2 1/7] sched: Add static_key for asymmetric cpu capacity optimizations
Date
The existing asymmetric cpu capacity code should cause minimal overhead
for others. Putting it behind a static_key, it has been done for SMT
optimizations, would make it easier to extend and improve without
causing harm to others moving forward.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
kernel/sched/fair.c | 3 +++
kernel/sched/sched.h | 1 +
kernel/sched/topology.c | 9 +++++++++
3 files changed, 13 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3582117e1580..e4ce572113a9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6385,6 +6385,9 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
{
long min_cap, max_cap;

+ if (!static_branch_unlikely(&sched_asym_cpucapacity))
+ return 0;
+
min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 22909ffc04fb..017f62069e0b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1140,6 +1140,7 @@ DECLARE_PER_CPU(int, sd_llc_id);
DECLARE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
DECLARE_PER_CPU(struct sched_domain *, sd_numa);
DECLARE_PER_CPU(struct sched_domain *, sd_asym);
+extern struct static_key_false sched_asym_cpucapacity;

struct sched_group_capacity {
atomic_t ref;
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 64cc564f5255..b023a5b3665a 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -398,6 +398,7 @@ DEFINE_PER_CPU(int, sd_llc_id);
DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
DEFINE_PER_CPU(struct sched_domain *, sd_numa);
DEFINE_PER_CPU(struct sched_domain *, sd_asym);
+DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);

static void update_top_cache_domain(int cpu)
{
@@ -425,6 +426,12 @@ static void update_top_cache_domain(int cpu)
rcu_assign_pointer(per_cpu(sd_asym, cpu), sd);
}

+static void update_asym_cpucapacity(int cpu)
+{
+ if (lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY))
+ static_branch_enable(&sched_asym_cpucapacity);
+}
+
/*
* Attach the domain 'sd' to 'cpu' as its base domain. Callers must
* hold the hotplug lock.
@@ -1705,6 +1712,8 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att

cpu_attach_domain(sd, d.rd, i);
}
+
+ update_asym_cpucapacity(cpumask_first(cpu_map));
rcu_read_unlock();

if (rq && sched_debug_enabled) {
--
2.7.4
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